A photographic emulsion is disclosed comprised of a dispersing medium and radiation-sensitive grains with greater than 50 percent of total grain projected area being accounted for by tabular grains comprised of (1) a tabular host portion containing greater than 50 mole percent bromide, based on silver, and having spaced parallel {111} major faces, (2) a first epitaxial phase containing greater than 90 mole percent iodide, based on silver, accounting for less than 60 percent of total silver and overlying from 15 to 90 percent of the major faces, and (3) surface silver halide of a face centered cubic crystal lattice structure overlying at least a portion of the first epitaxial phase.
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1. A photographic emulsion comprised of a dispersing medium and radiation-sensitive silver halide grains with greater than 50 percent of total grain projected area being accounted for by tabular grains comprised of
a tabular host portion containing greater than 50 mole percent bromide, based on silver, and having spaced parallel {111} major faces, a first epitaxial phase containing greater than 90 mole percent iodide, based on silver, accounting for less than 60 percent of total silver and overlying from 15 to 90 percent of the major faces, and surface silver halide of a face centered cubic rock salt crystal lattice structure overlying at least a portion of the first epitaxial phase.
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The invention is directed to an improvement in photographic emulsions containing radiation-sensitive intermediate and higher aspect ratio tabular grains.
In referring to silver halide emulsions, grains and grain regions containing two or more halides, the halides are named in order of ascending concentrations.
All references to the mole percentages of a particular halide in silver halide are based on total silver present in the grain region, grain or emulsion being discussed.
The term "high bromide" in referring to a grain region, grain or emulsion indicates greater than 50 mole percent bromide, based on silver.
The term "high iodide" in referring to a grain region, grain or emulsion indicates greater than 90 mole percent iodide, based on silver.
The symbol "μm" employed to denote micrometers.
The "equivalent circular diameter" (ECD) of a grain is diameter of a circle having an area equal to the projected area of the grain.
The "aspect ratio" of a silver halide grain is the ratio of its ECD divided by its thickness (t).
The "average aspect ratio" of a tabular grain emulsion is the quotient of the mean ECD of the tabular grains divided by their mean thickness (t).
The term "tabular grain" is defined as a grain having an aspect ratio of at least 2.
The term "tabular grain emulsion" is defined gas an emulsion in which at least 50 percent of total grain projected area is accounted for by tabular grains.
The terms "thin" and "ultrathin" in referring to tabular grains and emulsions are employed to indicate tabular grains having thickness of <0.2 μm and <0.07 μm, respectively.
The term "dopant" refers to a material other than silver or halide ion contained in a silver halide crystal lattice structure.
All periods and groups of elements are assigned based on the periodic table adopted by the American Chemical Society and published in the Chemical and Engineering News, Feb. 4, 1985, p. 26, except that the term "Group VIII" is employed to designate groups 8, 9 and 10.
The term "meta-chalcazole" is employed to indicate the following ring structure: ##STR1## where X is one of the chalcogens: O, S or Se.
All spectral sensitizing dye oxidation and reduction voltages were measured in acetonitrile against a Ag/AgCl saturated KCl electrode, as described in detail by J. Lenhard J. Imag. Sci., Vol. 30, #1, p. 27, 1986. Where oxidation or reduction potentials for spectral sensitizing dyes were estimated, the method employed was that described by S. Link "A Simple Calculation of Cyanine Dye Redox Potentials", Paper F15, International East-West Symposium II, Oct. 30-Nov. 4, 1988.
The term "inertial speed" refers to the speed of a silver halide emulsion determined from its characteristic curve (a plot of density vs. log E, where E represents exposure in lux-seconds) as the intersection of an extrapolation of minimum density to a point of intersection with a line tangent to the highest contrast portion of the characteristic curve. The inertial speed is the reciprocal of the exposure at the point of intersection noted above.
Speeds are reported as relative log speeds, where a speed difference of 1 represents a difference of 0.01 log E, where E is exposure in lux-seconds.
Research Disclosure is published by Kenneth Mason Publications, Ltd., Dudley House, 12 North St., Emsworth, Hampshire P010 7DQ, England.
Maskasky U.S. Pat. Nos. 4,094,684, 4,142,900 and 4,158,565 (collectively referred to as Maskasky I) disclose emulsions in which silver chloride is epitaxially deposited on nontabular silver iodide host grains. These patents are generally credited as the first suggestion that a silver iodide phase can be relied upon for photon capture while a developable latent image is formed in an epitaxially joined lower iodide portion of the grain. When a photon is captured within the iodide portion of the grain, a hole (photohole) and a conduction band electron (photoelectron) pair are created. The photoelectron migrates across the epitaxial junction to form a latent image in the lower iodide portion of the grain. On the other hand, the photohole remains trapped within the silver iodide phase. Thus, the risk of dissipation of absorbed photon energy by hole-electron recombination is minimized. House U.S. Pat. No. 4,490,458 and Maskasky U.S. Pat. No. 4,459,353 (collectively referred to as House and Maskasky) later placed silver chloride epitaxy on silver iodide tabular grains to combine the advantages of Maskasky I with those known to flow from a tabular grain configuration. Although the Maskasky I and the House and Maskasky emulsions offer superior performance compared to emulsions with grains consisting essentially of a high iodide silver halide phase, the performance of none of these emulsions has been sufficiently attractive to lead to commercial use in photography. The ratio of iodide to the remaining halide(s) is unattractively high while photographic speed and developability, though superior to grains consisting essentially of a high iodide silver halide phase, are slow.
Between the investigations of Maskasky I and those of House and Maskasky, a marked advance took place in silver halide photography based on the discovery that a wide range of photographic advantages, such as improved speed-granularity relationships, increased covering power both on an absolute basis and as a function of binder hardening, more rapid developability, increased thermal stability, increased separation of native and spectral sensitization imparted imaging speeds, and improved image sharpness in both mono- and multi-emulsion layer formats, can be realized by increasing the proportions of selected tabular grain populations in photographic emulsions. The tabular grains were initially selected to have a high (>8) average aspect ratio or at least an intermediate (5-8) average aspect ratio. The tabular grains were those having a face centered cubic rock salt crystal lattice structure (hereinafter referred to as an FCCRS crystal lattice structure), which a high iodide silver halide composition does not form, except under extreme conditions having no relevance to photography. Silver chloride, silver bromide and mixtures thereof in all ratios form an FCCRS crystal lattice structure. An FCCRS crystal lattice can accommodate minor amounts of iodide. The highest reported levels of photographic performance have been obtained with tabular grain emulsions containing silver iodobromide grains. Early disclosures of high and intermediate aspect ratio tabular grain emulsions with FCCRS crystal lattices are illustrated by Kofron et al U.S. Pat. No. 4,439,520, Wilgus et al U.S. Pat. No. 4,434,226 and Abbott et al U.S. Pat. Nos. 4,425,425 and 4,425,426.
High aspect ratio silver iodobromide tabular grains containing non-uniform iodide distributions are disclosed by Solberg et al U.S. Pat. No. 4,433,048, Ikeda et al U.S. Pat. No. 4,806,461, Nakamura et al U.S. Pat. No. 5,096,806, Piggin et al U.S. Pat. Nos. 5,061,609 and 5,061,616, and Suga et al U.S. Pat. No. 5,418,124. Generally (but not always) iodide has been incorporated in the grains in the FCCRS crystal lattices, and the highest iodide concentrations have been restricted to the edges or corners of the grains.
Reed and Hansen U.S. Ser. No. 08/620,773, Mar. 22, 1996, now U.S. Pat. No. 5,604,086, commonly assigned, titled TABULAR GRAIN EMULSIONS CONTAINING A RESTRICTED HIGH IODIDE SURFACE PHASE, discloses a photographic emulsion comprised of a dispersing medium and radiation-sensitive silver halide grains with greater than 50 percent of total grain projected area being accounted for by grains containing a host portion of a face centered cubic rock salt crystal lattice structure and a first epitaxial phase containing greater than 90 mole percent iodide. The host portion is tabular, being bounded by an exterior having first and second parallel major faces joined by a peripheral edge. The first epitaxial phase accounts for less than 60 percent of total silver, and the first epitaxial phase is restricted to a portion of the exterior of the host portion that includes at least 15 percent of the major faces.
Reed and Hansen U.S. Ser. No. 08/697,811, filed concurrently herewith and commonly assigned, titled HIGH CHLORIDE {100} TABULAR GRAIN EMULSIONS CONTAINING A HIGH IODIDE INTERNAL EPITAXIAL PHASE, discloses a photographic emulsion comprised of high chloride radiation-sensitive tabular grains comprised of a tabular host portion containing greater than 50 mole percent chloride, based on silver, and having spaced parallel {100} major faces, a high chloride shell accounting for at least 4 percent of total silver surrounding the host portion and, interposed between the shell and the host portion an internal epitaxial phase containing greater than 90 mole percent iodide, based on silver, overlying from 15 to 90 percent of the major faces of the host portion.
Problem to be Solved
Notwithstanding the many advances imparted to photographic imaging by FCCRS crystal lattice tabular grains, some shortcomings have been observed. FCCRS crystal lattice tabular grains work best when applied to minus blue (green and/or red) imaging, since they provide large surface areas in relation to grain volume for minus blue absorbing spectral sensitizing dyes. The silver halide itself lacks native minus blue sensitivity; hence reducing silver coating coverages while maintaining large surface areas for spectral sensitizing dye adsorption saves silver with little negative impact on imaging.
By comparison, the application of FCCRS crystal lattice tabular grains to forming blue exposure records has lagged. The reason is that traditionally the native blue sensitivity of has been heavily relied upon for latent image formation, even when blue spectral sensitizing dyes have been employed in combination with the grains. Attempts to realize the silver savings in blue recording emulsion layers that are routinely realized in minus blue recording emulsion layers by employing FCCRS crystal lattice tabular grains have resulted in speed penalties. The problem is exacerbated by the fact that, while daylight contains an equal amount of its total energy in the blue, green and red regions of the visible spectrum, blue photons contain more energy than either green and red photons; hence, daylight has available fewer blue photons than green or red photons for latent image formation. The problem cannot be corrected by simply increasing the levels of blue spectral sensitizing dye, since additional speed enhancement is not realized by dye additions beyond those that can be adsorbed to the grain surfaces. Kofron et al suggests increasing the maximum thickness of tabular grains from 0.3 μm to 0.5 μm to enhance their blue absorption. In the highest speed multicolor photographic elements it is common for the fastest minus blue recording emulsion layers to be formed using tabular grain emulsions while the fastest blue recording emulsion layer employs nontabular grains. Since the highest speed blue recording layer is typically the first emulsion layer to receive exposing radiation, there is a significant negative impact by the nontabular grains on the sharpness of the images in all of the remaining emulsion layers.
Another problem inherent in the conventional choices of FCCRS crystal lattice tabular grains is that the techniques disclosed by Maskasky I for photohole and photoelectron separation, with attendant reduction in their recombination, have been largely unrealized. These conventional tabular grains either contain no high iodide silver halide phase or have limited its extent to the edges or corners of the tabular grains.
In one aspect this invention is directed to a photographic emulsion comprised of a dispersing medium and radiation-sensitive silver halide grains with greater than 50 percent of total grain projected area being accounted for by tabular grains comprised of a tabular host portion containing greater than 50 mole percent bromide, based on silver, and having spaced parallel {111} major faces, a first epitaxial phase containing greater than 90 mole percent iodide, based on silver, accounting for less than 60 percent of total silver and overlying from 15 to 90 percent of the major faces, and surface silver halide of a face centered cubic rock salt crystal lattice structure overlying at least a portion of the first epitaxial phase.
FIG. 1 is a schematic plan view of a tabular grain satisfying the requirements of the invention.
FIG. 2 is a schematic sectional view along section line 2--2 in FIG. 1.
FIGS. 3, 6 and 9 are plots of percent light. absorption as a function of wavelength.
FIGS. 4 and 5 are transmission electron micrographs of the face and edges, respectively, of tabular grains from an emulsion according to the invention.
FIGS. 7 and 8 are transmission electron micrographs of the face and edges, respectively, of tabular grains from another emulsion according to the invention.
FIG. 10 is a plot of speed in 1/ergs/cm2 /sec versus wavelength.
At least 50 percent of the total grain projected area of emulsions according to the invention is accounted for by composite silver halide grains having at least three components: (1) a high bromide {111} tabular host portion, (2) a first epitaxial phase restricted to only a portion of the host exterior, but overlying at least 15 (preferably 25) percent to 90 percent of the {111} major faces of the host tabular grains, and (3) surface silver halide of a face centered cubic rock salt (FCCRS) structure overlying at least a portion of the first epitaxial phase.
The composite grain structure can be appreciated by reference to FIGS. 1 and 2. A composite tabular grain structure 100 is shown in FIG. 2 as a section along 2--2 in FIG. 1. An FCCRS crystal lattice shell 101 is shown in FIG. 2, but in FIG. 1 the shell is omitted, so that the remaining structure of the composite grain can be more easily appreciated. A tabular host portion 102 is provided by a high bromide {111} tabular grain having major faces 104 and 106. Epitaxially grown on the major faces are discrete plates 110, schematically shown as triangular and hexagonal domains (see FIG. 4 for an actual grain comparable to schematic FIG. 1), containing greater than 90 mole percent iodide. A feature to note is that the domains overlie at least 15 (preferably 25) to 90 percent of the major faces. As demonstrated in the Examples below the amount of surface silver halide can be restricted to such an extent it is no longer capable of forming a continuous shell, as preferred. However, so long as the surface silver halide overlies at a portion of the domains 110 benefits can still be derived from the presence of the surface silver halide.
As is well understood in the art, tabular grains are oriented with their major faces approximately normal to the direction of light transmission during imagewise exposure in a photographic element. When the grain 100 is exposed to light in the short (400 to 450 nm) blue region of the spectrum, photons are initially absorbed preferentially (and in some cases entirely) in the plates 110 on the major faces 104 and 106 of the tabular host portion 102. The plates on both the major face nearer to and farther from the source of exposing short blue light actively absorb short blue photons, since the shell and tabular host portion, each having an FCCRS crystal lattice, cannot absorb more than a small fraction of the exposing short blue light and unabsorbed light is transmitted through the tabular host portion.
Measured along the section line 2--2, the plates as shown in FIG. 2 overlie 35% of the upper major face and 48% of the lower major face. Notice that the plates on the upper and lower major faces are not aligned. At some points a short blue photon encounters no plate in passing through the composite grain, in other areas one plate, and in remaining areas two plates. As shown the upper and lower plates are positioned to intercept 71% of photons incident along section line 2--2.
It should be noticed that location of the plates on the major faces of the tabular host portion is an ideal orientation for short blue photon absorption. In this orientation the plates present a maximum target area for the photons. If the plates were instead located entirely on the peripheral edge 108 of the tabular host grain portion, they would present a much smaller target area and fewer short blue photons would be absorbed. Although the ideal is to eliminate edge plates, as shown, it is recognized that in practice plates are usually located to some extent on both the edge and major face surfaces of the tabular host portions. However, techniques are described below for minimizing the proportion of the plates located along the peripheral edge.
If, instead of forming a high iodide silver halide phase on the surface of the tabular host portion, the tabular host portion is simply optimally sensitized with a spectral sensitizing dye having a short blue absorption maxima (hereinafter referred to as a short blue spectral sensitizing dye), the highest blue light absorption attainable without desensitization is still much less than that which can be obtained by employing the internal epitaxial phase as described. Maximum light absorption by an optimally spectrally sensitized tabular grain is typically in the 10 to 15 percent range. By contrast, the high iodide epitaxial phase can produce short blue light absorptions in each grain that are well in excess of 50 percent. Since in emulsion coatings the path of exposing radiation intercepts a plurality of grains, it is appreciated that capture of short blue photons can approach 100 percent when the emulsions of the invention are employed. Nevertheless, to reduce the amount of silver required in coating, it is specifically contemplated, as one alternative, to employ an emulsion according to the invention in combination with one or more conventional short blue spectral sensitizing dyes.
When a blue spectral sensitizing dye (a dye having an absorption maximum in the 400-500 nm spectral region) is selected for a conventional tabular grain emulsion, a theoretically ideal choice is a dye having a half-peak bandwidth (a spectral wavelength range over which it exhibits an absorption of at least half its maximum absorption) of 100 nm, extending from 400 to 500 nm. In practice, few spectral sensitizing dyes exhibit 100 nm half peak bandwidths, nor are actual half peak bandwidths coextensive with the blue region of the spectrum. Typical blue spectral sensitizing dyes exhibit half peak bandwidths of less than 50 nm.
In a specifically preferred form of the invention it is contemplated to employ emulsions according to the invention in combination with one or more spectral sensitizing dyes having an absorption maxima in the long blue (450-500 nm) region of the spectrum (hereinafter referred to as a long blue spectral sensitizing dye). The high iodide silver halide provided by the internal epitaxial phase offers peak absorption near 425 nm. When this absorption is combined with that provided by a long blue spectral sensitizing dye, a higher blue absorption over the entire blue portion of the spectrum is realized.
It is, of course, possible to employ combinations of short and long blue spectral sensitizing dyes with the tabular grain emulsions of the invention. Assuming dyes are selected of equal efficiencies, when this is undertaken, the proportion of total sensitivity provided by the combination of blue spectral sensitizing dyes is no higher and usually somewhat less than that which can be obtained by employing the long blue spectral sensitizing dye alone.
When, in the absence of a spectral sensitizing dye, a short blue photon is absorbed by a plate, a photohole and a photoelectron pair are created. The photoelectron is free to migrate across the epitaxial junction into the tabular host portion. On the other hand, the photohole is trapped within the plate. What therefore occurs is separation of the photoelectron from the photohole, which in turn minimizes the risk of their mutual annihilation by recombination. Thus, the plates contribute to larger numbers of photoelectrons being available for latent image formation and enhance the overall sensitivity of the emulsion grains.
When a spectral sensitizing dye of any absorption maxima is employed in combination with the composite grains of the invention containing surface silver halide in an amount sufficient to form a shell, at least 4 mole percent, based on total silver, the dye selection extends to the full range of conventional choices of spectral sensitizing dyes. This includes spectral sensitizing dyes extending over the entire useful range of from -0.86 volt to the most negative observed reduction potentials, up to about -2.0 volts. On the other hand, where the surface silver halide is only partially interposed between the high iodide plates and the spectral sensitizing dye, it is necessary that the spectral sensitizing dye to exhibit a reduction potential more positive than -1.30 volts for electron injection to occur from the dye directly into the high iodide plates. In the absence of a shell--e.g., with surface silver halide concentrations ranging from about 1 to less than 4 mole percent, based on total silver, it is preferred to choose spectral sensitizing dyes having reduction potentials in the range of from -0.86 to -1.30 volts. When the surface silver halide forms a shell--that is, with surface silver halide concentrations of at least 4 mole percent, the same spectral sensitizing dyes can be employed as well as all other conventional spectral sensitizing dyes, including the common spectral sensitizing dyes having reduction potentials in the range of from -1.35 to -1.80 volts.
The emulsions of the invention can be prepared by starting with any conventional high bromide {111} tabular grain emulsion. The starting tabular grains can consist essentially of silver bromide, silver chlorobromide, silver iodobromide, silver iodochlorobromide or silver chloroiodobromide.
The high (>50 mole %) bromide starting tabular grain emulsions preferably contain greater than 70 (optimally >90) mole percent bromide, based on silver, with chloride preferably limited to 10 mole % or less, based on silver. Silver bromide is less soluble than silver chloride and therefore more resistant to halide displacement from the FCCRS crystal lattice structure on subsequent epitaxial deposition. Iodide inclusions in the starting tabular grains are preferably less than 10 mole percent, since the high iodide silver halide first epitaxial phase is capable of performing the imaging functions normally accomplished by high iodide inclusions. When iodide is included in the starting tabular grains, it can be uniformly or nonuniformly distributed in any conventional manner.
The starting tabular grains have {111} major faces (elsewhere referred to as {111} tabular grains) usually have triangular or hexagonal major faces. Generally, the more uniform the tabular grain population, the higher the proportion of tabular grains with hexagonal major faces. In their most highly controlled forms {111} tabular grains with adjacent edges of hexagonal major faces that differ in length by less than 2:1 account for greater than 90 percent of the total tabular grains. Corner rounding due to ripening typically ranges from barely perceptible to creating almost circular major faces.
The starting tabular grain emulsions can have any photographically useful mean ECD, typically up to 10 μm, but preferably the tabular grain emulsions have a mean ECD of 5 μm or less. The starting tabular grains can have any thickness, ranging from the minimum reported thicknesses for ultrathin (<0.07 μm) tabular grain emulsions up to the maximum thickness compatible with a >5 average aspect ratio. It is generally preferred that the starting tabular grains have a thickness of less than 0.3 μm, more preferably, less than 0.2 μm, and, most preferably less than 0.07 μm.
The tabular grains of the starting emulsions (preferably those having a thickness of <0.3 μm, more preferably <0.2 μm, and most preferably <0.07 μm) account for greater than 50 percent, preferably greater than 70 percent and most preferably greater than 90 percent of total grain projected area. In specifically preferred starting tabular grain emulsions substantially all (greater than 97 percent) of total grain projected area can be accounted for by tabular grains.
The starting tabular grain emulsion can exhibit any conventional level of dispersity, but preferably exhibits a low level of dispersity. It is preferred that the starting tabular grain emulsion exhibit a coefficient of variation (COV) of grain diameter of less than 30 percent, most preferably less than 25 percent. Conventional starting tabular grain emulsions are known having a COV of less than 10 percent. Grain COV is herein defined as 100 times the standard deviation of grain ECD divided by mean grain ECD.
Conventional high bromide {111} tabular grain emulsions are illustrated by the following:
Abbott et al U.S. Pat. No. 4,425,425;
Abbott et al U.S. Pat. No. 4,425,426;
Wilgus et al U.S. Pat. No. 4,434,226;
Kofron et al U.S. Pat. No. 4,439,520;
Daubendiek et al U.S. Pat. No. 4,414,310;
Solberg et al U.S. Pat. No. 4,433,048;
Yamada et al U.S. Pat. No. 4,647,528;
Sugimoto et al U.S. Pat. No. 4,665,012;
Daubendiek et al U.S. Pat. No. 4,672,027;
Yamada et al U.S. Pat. No. 4,678,745;
Maskasky U.S. Pat. No. 4,684,607;
Yagi et al U.S. Pat. No. 4,686,176;
Hayashi U.S. Pat. No. 4,783,398;
Daubendiek et al U.S. Pat. No. 4,693,964;
Maskasky U.S. Pat. No. 4,713,320;
Nottorf U.S. Pat. No. 4,722,886;
Sugimoto U.S. Pat. No. 4,755,456;
Goda U.S. Pat. No. 4,775,617;
Saitou et al U.S. Pat. No. 4,797,354;
Ellis U.S. Pat. No. 4,801,522;
Ikeda et al U.S. Pat. No. 4,806,461;
Ohashi et al U.S. Pat. No. 4,835,095;
Makino et al U.S. Pat. No. 4,835,322;
Bando U.S. Pat. No. 4,839,268;
Daubendiek et al U.S. Pat. No. 4,914,014;
Aida et al U.S. Pat. No. 4,962,015;
Saitou et al U.S. Pat. No. 4,977,074;
Ikeda et al U.S. Pat. No. 4,985,350;
Piggin et al U.S. Pat. No. 5,061,609;
Piggin et al U.S. Pat. No. 5,061,616;
Takehara et al U.S. Pat. No. 5,068,173;
Nakemura et al U.S. Pat. No. 5,096,806;
Bell et al U.S. Pat. No. 5,132,203;
Tsaur et al U.S. Pat. No. 5,147,771;
Tsaur et al U.S. Pat. No. 5,147,772;
Tsaur et al U.S. Pat. No. 5,147,773;
Tsaur et al U.S. Pat. No. 5,171,659;
Tsaur et al U.S. Pat. No. 5,210,013;
Antoniades et al U.S. Pat. No. 5,250,403;
Kim et al U.S. Pat. No. 5,272,048;
Sutton et al U.S. Pat. No. 5,334,469;
Black et al U.S. Pat. No. 5,334,495;
Chaffee et al U.S. Pat. No. 5,358,840;
Delton U.S. Pat. No. 5,372,927; and
Zola and Bryant EPO 0 362 699.
The first epitaxial phase deposited on the starting tabular grains (the host tabular grain portions of the resulting composite grains) contains at least 90, preferably at least 95, mole percent iodide. The remaining halide is typically bromide. The inclusion of minor amounts of halides other than iodide is typically the result of undertaking precipitation of the epitaxial phase by silver and iodide ion introduction into the starting tabular grain emulsion in the presence of bromide and/or chloride ions in the dispersing medium of the starting tabular grain emulsion that are in equilibrium with the tabular grains. Bromide and/or chloride ion inclusion can be limited by limiting their availability and is in all instances limited by the inability of the bromide and/or chloride ions to incorporate into the crystal lattice structure of the epitaxial phase, which is not an FCCRS crystal lattice structure, in concentrations of greater than 10 mole percent.
Silver iodide under conditions relevant to emulsion precipitation is generally reported to form either a hexagonal wurtzite (β phase) or face centered cubic zinc blend type (γ phase) silver iodide phase. Depending upon the specific precipitation conditions selected it is believed that the first epitaxial phase can be any one or a combination of these phases.
The first epitaxial phase preferably accounts for less than 25, more preferably less than 20 and, in most instances, less than 10, percent of the total silver forming the composite grains. The minimum amount of silver contained in the first epitaxial phase is determined by the requirement that this phase be located on at least 25 percent of the major faces of the host tabular grains. Fortunately, it has been discovered that the first epitaxial phase can be deposited on the major faces in the form of thin plates, preferably having thicknesses in the range of from 50 nm (0.05 μm) to 1 nm (0.001 μm). Thus, very small amounts of silver in the first epitaxial phase are capable of occupying a large percentage of the major faces of the host tabular grains.
As the thickness of the host tabular grains decreases, it is appreciated that the percentage of total silver provided by the first epitaxial phase increases, even when the thickness of the plates and the percentage of the total surface they occupy remains the unchanged. Thus, with ultrathin (<0.07 mean ECD) host tabular grains, it is contemplated that nearly 60 percent of the total silver forming the composite grains can be provided by first epitaxial phase. However, even using ultrathin host tabular grain emulsions, it is preferred to limit the first epitaxial phase to less than 50 percent of total silver forming the composite grains.
Exactly how thick the plates of the first epitaxial phase should be and what percentage of total major face coverage should be sought for optimum performance depends upon the function that the first epitaxial phase is required to perform. If an emulsion of the invention is intended to be employed primarily for absorbing short blue light on exposure, short blue light absorption increases as the thickness of the plates is increased and as the percentage of the major faces of the host tabular grains occupied is increased. At 427 nm, the absorption maxima of silver iodide, the portion of a silver iodide epitaxial phase on the upper major faces of the host tabular grains is capable of absorbing 63 percent of the photons it receives when the epitaxial phase thickness is 50 nm, and 86 percent of the photons passing through the silver iodide epitaxial phase located on both major faces of the host tabular grains are absorbed. These short blue absorptions are so much higher than those of the silver iodobromides and blue spectral sensitizing dyes conventionally used for short blue absorption, it is apparent that the plates can be much thinner than 50 nm and still offer advantageous short blue light absorption. Further, it must be kept in mind that at conventional silver coating coverages of silver halide emulsions several tabular grains are positioned to intercept a photon received at any one point. To distribute short blue light absorption within the grain population and thereby use the grains to maximum advantage it is preferred to decrease the thickness of the plates to less than 25 nm, most preferably less than 10 nm, while increasing the percentage of the host tabular grain major surfaces they overlie. It is preferred that the plates occupy at least 50, most preferably at least 70, percent of the major faces of the host tabular grains.
It should be specifically noted that the probability of a short blue photon being transmitted through an emulsion layer containing grains according to the invention can be reduced to such a low level that the common problem of blue punch through can be virtually non-existent. Stated another way, short blue light penetrating the emulsion layer can be reduced to such low levels that common protective approaches, such as yellow (blue absorbing) filter layers to protect underlying minus blue recording layers from blue light exposure can be omitted without incurring any significant imaging penalty.
If, instead of short blue absorption, the emulsions of the invention are employed in combination with a minus blue spectral sensitizing dye with the function of the high iodide silver halide epitaxial phase being limited to providing a trap for photoholes, then both the thickness and the percentage of major face coverage of the plates can be reduced. Only a minimal thickness is required for a plate to function as a hole trap. At the same time, if the plate is not located to intercept a photon, it can still act as a hole trap, since lateral migration of holes and electrons within the FCCRS crystal lateral structure is more than adequate to allow this to occur. However, for maximum imaging efficiency it is still preferred that the plates occupy at least 25 percent of the major faces of the host tabular grains.
For the composite grains to maintain high levels of imaging efficiency it is essential that the high iodide silver halide epitaxial phase be restricted to only a portion of the host tabular grain exterior surfaces. In the absence of further composite grain modifications to place latent image, described below, latent image sites are formed in the host tabular grains. By contrast, development of a conventional core-shell grain containing a high iodide silver halide shell requires that development begin at a high iodide surface of the grain, thereby releasing relatively high levels of iodide ion to solution that can slow or arrest the rate of subsequent development. It is preferred that the high iodide silver halide epitaxy cover no more than 90 percent of the exterior of the host tabular grains.
Since, in the absence of the high iodide silver halide epitaxy, the edges of the host tabular grains are the favored locations for latent image formation, it is preferred to leave as much of the peripheral edge of the host tabular grains free of the high iodide silver halide epitaxy as possible. For example, where only a small fraction of the total exterior of the host tabular grains is free of the high iodide silver halide epitaxy, it is preferred that the largest possible portion of this small fraction be located at the edges of the host tabular grains.
It has been discovered quite unexpectedly that depositing the high iodide silver halide epitaxy on the host tabular grains as plates is easily accomplished only when the high iodide silver halide phase is precipitated by controlled double jet precipitation. Attempts to grow silver iodide plates over the major surfaces of host tabular grains by ripening out silver iodide Lippmann grains have not been entirely successful, often resulting in large plates that extend outwardly beyond the periphery of the host tabular grains.
For successful high iodide plate formation on the major faces of the host tabular grains it has been discovered that both the iodide and bromide ion concentrations in the dispersing medium surrounding the grains must be controlled during formation of the high iodide first epitaxial phase. To appreciate the parameters involved it is first necessary to recognize that silver halide (AgX, where X represents any photographically useful halide) exists in a photographic emulsion in equilibrium with its component ions. This is illustrated as follows:
(I) ##STR2##
While at equilibrium almost all of the silver and halide ions are present in the AgX crystal structure, a low level of Ag+ and X- remain in solution. At any given temperature the activity product of Ag+ and X- is, at equilibrium, a constant and satisfies the relationship :
Ksp =[Ag+ ][X- ] (II)
where
[Ag+ ] represents the equilibrium silver ion activity,
[X- ] represents the equilibrium halide ion activity, and
Ksp is the solubility product constant of the silver halide.
To avoid working with small fractions, the following relationship is also widely employed:
-log Ksp =pAg+pX (III)
where
pAg represents the negative logarithm of the equilibrium silver ion activity and
pX represents the negative logarithm of the equilibrium halide ion activity.
The solubility product constants of the photographic silver halides are well known. The solubility product constants of AgCl, AgBr and AgI over the temperature range of from 0° to 100°C are published in Mees and James, The Theory of the Photographic Process, 3rd Ed., Macmillan, 1966, at page 6. Specific values are provided in Table I.
| TABLE I |
| ______________________________________ |
| Temperature |
| AgCl AgI AgBr |
| °C. |
| logKsp |
| logKsp |
| logKsp |
| ______________________________________ |
| 40 9.2 15.2 11.6 |
| 50 8.9 14.6 11.2 |
| 60 8.6 14.1 10.8 |
| 70 8.3 -- 10.5 |
| 80 8.1 13.2 10.1 |
| 90 7.6 -- 9.8 |
| ______________________________________ |
In preparing photographic emulsions the relative amounts of Ag+ are maintained less than those of X- to avoid fogging the emulsion. The relationship in which the concentrations of Ag+ and X- in solution are equal is referred to as the equivalence point. The equivalence point is the pX of the most soluble halide present that is exactly half the -logKsp of the corresponding silver halide.
To minimize the risk of halide conversion occurring in the host tabular grains during precipitation of the high iodide plates it is contemplated to limit the concentration of iodide ion in the dispersing medium during precipitation to a pI of greater than 4∅ Lower levels of iodide in solution ranging to a pI of 9.5 are contemplated. A preferred pI range of is from about 4.5 to 9∅
To maximize major face deposition of the high iodide epitaxy and minimize peripheral edge deposition it is preferred that the concentration of the remaining halide ion in solution (e.g., bromide) be maintained between a concentration of minimum solubility and the equivalence point. For example, for a high bromide host tabular grain emulsion, it is preferred to maintain the pBr of the dispersing medium in the range of from 3.3 and 5.4 at 60°C
Normally high bromide tabular grain emulsions are precipitated with a large halide ion excess. The halide ion concentration in solution is well above its minimum solubility concentration. Silver bromide tabular grains are typically precipitated at pBr values below 3.0, while silver chloride tabular grains are typically precipitated at pCl values of less than 2.4. Thus adjustment of the remaining halide ion concentrations in solution, in addition to introducing concurrently iodide and silver ions, is contemplated for deposition of the high iodide epitaxy preferentially onto the major faces of the host tabular grains.
In FIGS. 1 and 2 the high iodide epitaxy is shown as discrete triangular or hexagonal plates. In fact, under the conditions that most favor major face deposition, the high iodide epitaxy loses its linear boundaries, with adjacent plates often merging, as shown in FIG. 7.
Following deposition of the first epitaxial phase, surface silver halide of an FCCRS crystal lattice structure is deposited to overlie at least a portion of the first epitaxial phase. Any amount of surface silver halide capable of enhancing performance, typically at least 1 percent of total silver, is contemplated. It is preferred that sufficient surface silver halide be present in the composite tabular grains to form a shell over the first epitaxial phase. The shell preferably accounts for at least 4 (most preferably 8) percent of total silver. Shell thickness accounting for less than 20 percent of total silver are contemplated in all instances. Preferably the shell accounts for less than 15 percent of total silver.
The surface silver halide can be of any composition capable of providing an FCCRS crystal lattice structure. Preferably the shell contains less than 10 mole percent iodide, based on silver. The surface of the shell preferably contains less than 3 mole percent iodide, based on silver. In one specifically preferred form the surface silver halide is formed by the double-jet addition of silver bromide, with any iodide inclusion being derived from the first epitaxial phase. In another specifically contemplated form chloride can wholly or partially replace bromide during double-jet addition. Silver chloride at the surface of the composite tabular grains offers the advantage of higher initial rates of development.
Since both the first epitaxial phase and shell can be quite thin and account for only a small percentage of total silver, it is apparent that the various numerical parameters (e.g., aspect ratio, ECD, COV, and percent of total grain projected area) stated above for the starting tabular grain emulsions can also be satisfied by the composite tabular grains.
A preferred sensitization for the emulsions of the invention is to effect a second epitaxial deposition onto the composite tabular grains after the first epitaxial phase has been precipitated. The epitaxial phase can be formed by the epitaxial precipitation of one or more silver salts on a host grain of a differing composition at selected surface sites, as illustrated by Maskasky U.S. Pat. Nos. 4,094,684, 4,435,501, 4,463,087, 4,471,050 and 5,275,930, Ogawa U.S. Pat. No. 4,735,894, Yamashita et al U.S. Pat. No. 5,011,767, Haugh et al U.K. Pat. No. 2,038,792, Koitabashi EPO 0 019 917, Ohya et al EPO 0 323 215, Takada EPO 0 434 012, Chen EPO 0 498 302 and Berry and Skillman, "Surface Structures and Epitaxial Growths on AgBr Microcrystals", Journal of Applied Physics, Vol. 35, No. 7, Jul. 1964, pp. 2165-2169.
The preferred epitaxial sensitization of emulsions according to the invention containing high bromide host tabular grains is to deposit epitaxially silver chloride at the edges or, preferably, the corners of the tabular grains. Minor amounts, preferably less than 10 mole percent, based on total silver forming the second epitaxial phase) of silver bromide and iodide are incorporated into the epitaxy in addition to silver chloride. Although the silver chloride epitaxy can to some extent overlap adjacent high iodide plates, the high iodide plates tend to direct epitaxy to the host grain exterior surfaces. Hence, epitaxial junctions are formed between the second epitaxial phase at the exterior surfaces of the host tabular grains. When the host tabular grains are high chloride tabular grains, the second epitaxial phase is preferably a high bromide silver halide composition, such as silver bromide, optionally containing minor amounts of chloride and/or iodide, typically limited to 10 mole percent or less of the second epitaxial phase. Conventional chemical sensitization, such as sulfur and/or gold sensitization can, if desired, by combined with sensitization provided by the second epitaxial phase.
The second epitaxial phase when present preferably accounts for less than 25 (most preferably less than 10) percent of the total silver forming the composite grains. The second epitaxial phase is effective, even when it accounts for as little as 1 mole percent of total silver. Preferably the second epitaxial phase accounts for at least 2, optimally at least 5, percent of the total silver forming the composite grains.
A preferred technique for directing the second epitaxial phase to the edges and/or corners of the tabular grains is to employ a J aggregating spectral sensitizing dye as a site director, as taught by Maskasky U.S. Pat. No. 4,435,501. Maskasky '501 further teaches that surface iodide is capable of acting as a site director. Thus, the iodide in the first epitaxial phase assists in directing the second epitaxial phase to the edges and corners of the host tabular grains.
It is specifically contemplated to incorporate one or more dopants in the FCCRS crystal lattice structure of the composite tabular grains, either in the tabular host portion or in the shell. When two or more dopants are incorporated, it is specifically contemplated to place one dopant in the tabular host portion and another in the shell to avoid antagonistic effects that can occur when dissimilar dopants are present in the same grain region. Any conventional dopant known to be useful in an FCCRS crystal lattice can be incorporated. Photographically useful dopants selected from a wide range of periods and groups within the Periodic Table of Elements have been reported. Conventional dopants include ions from periods 3 to 7 (most commonly 4 to 6) of the Periodic Table of Elements, such as Fe, Co, Ni, Ru, Rh, Pd, Re, Os, Ir, Pt, Mg, Al, Ca, Sc, Ti, V, Cr, Mn, Cu, Zn, Ga, Ge, As, Se, Sr, Y, Mo, Zr, Nb, Cd, In, Sn, Sb, Ba, La, W, Au, Hg, Tl, Pb, Bi, Ce and U. The dopants can be employed (a) to increase the sensitivity, (b) to reduce high or low intensity reciprocity failure, (c) to increase, decrease or reduce the variation of contrast, (d) to reduce pressure sensitivity, (e) to decrease dye desensitization, (f) to increase stability (including reducing thermal instability), (g) to reduce minimum density, and/or (h) to increase maximum density. For some uses any polyvalent metal ion is effective. The following are illustrative of conventional dopants capable of producing one or more of the effects noted above when incorporated in the silver halide epitaxy: B. H. Carroll, "Iridium Sensitization: A Literature Review", Photographic Science and Engineering, Vol. 24, No. 6, November/December 1980, pp. 265-267; Hochstetter U.S. Pat. No. 1,951,933; De Witt U.S. Pat. No. 2,628,167; Spence et al U.S. Pat. No. 3,687,676 and Gilman et al U.S. Pat. No. 3,761,267; Ohkubo et al U.S. Pat. No. 3,890,154; Iwaosa et al U.S. Pat. No. 3,901,711; Yamasue et al U.S. Pat. No. 3,901,713; Habu et al U.S. Pat. No. 4,173,483; Atwell U.S. Pat. No. 4,269,927; Weyde U.S. Pat. No. 4,413,055; Menjo et al U.S. Pat. No. 4,477,561; Habu et al U.S. Pat. No. 4,581,327; Kobuta et al U.S. Pat. No. 4,643,965; Yamashita et al U.S. Pat. No. 4,806,462; Grzeskowiak et al U.S. Pat. No. 4,828,962; Janusonis U.S. Pat. No. 4,835,093; Leubner et al U.S. Pat. No. 4,902,611; Inoue et al U.S. Pat. No. 4,981,780; Kim U.S. Pat. No. 4,997,751; Shiba et al U.S. Pat. No. 5,057,402; Maekawa et al U.S. Pat. No. 5,134,060; Kawai et al U.S. Pat. No. 5,153,110; Johnson et al U.S. Pat. No. 5,164,292; Asami U.S. Pat. Nos. 5,166,044 and 5,204,234; Wu U.S. Pat. No. 5,166,045; Yoshida et al U.S. Pat. No. 5,229,263; Bell U.S. Pat. Nos. 5,252,451 and 5,252,530; Komorita et al EPO 0 244 184; Miyoshi et al EPO 0 488 737 and 0 488 601; Ihama et al EPO 0 368 304; Tashiro EPO 0 405 938; Murakami et al EPO 0 509 674 and 0 563 946 and Japanese Patent Application Hei-2[1990]-249588 and Budz WO 93/02390.
When dopant metals are present during precipitation in the form of coordination complexes, particularly tetra- and hexa-coordination complexes, both the metal ion and the coordination ligands can be occluded within the grains. Coordination ligands, such as halo, aquo, cyano, cyanate, fulminate, thiocyanate, selenocyanate, tellurocyanate, nitrosyl, thionitrosyl, azide, oxo, carbonyl and ethylenediamine tetraacetic acid (EDTA) ligands have been disclosed and, in some instances, observed to modify emulsion properties, as illustrated by Grzeskowiak U.S. Pat. No. 4,847,191, McDugle et al U.S. Pat. Nos. 4,933,272, 4,981,781 and 5,037,732, Marchetti et al U.S. Pat. No. 4,937,180, Keevert et al U.S. Pat. No. 4,945,035, Hayashi U.S. Pat. No. 5,112,732, Murakami et al EPO 0 509 674, Ohya et al EPO 0 513 738, Janusonis WO 91/10166, Beavers WO 92/16876, Pietsch et al German DD 298,320, Olm et al U.S. Pat. No. 5,360,712, and Kuromoto et al U.S. Pat. No. 5,462,849. Olm et al and Kuromoto et al, cited above, disclose hexacoordination complexes containing organic ligands while Bigelow U.S. Pat. No. 4,092,171 discloses organic ligands in Pt and Pd tetra-coordination complexes.
It is specifically contemplated to incorporate in the silver halide epitaxy a dopant to reduce reciprocity failure. Iridium is a preferred dopant for decreasing reciprocity failure. The teachings of Carroll, Iwaosa et al, Habu et al, Grzeskowiak et al, Kim, Maekawa et al, Johnson et al, Asami, Yoshida et al, Bell, Miyoshi et al, Tashiro and Murakami et al EPO 0 509 674, each cited above, are here incorporated by reference.
In another specifically preferred form of the invention it is contemplated to incorporate in the face FCCRS crystal lattice structure of the composite tabular grains a dopant capable of increasing photographic speed by forming shallow electron traps, hereinafter also referred to as a SET dopant. The selection criteria for SET dopants is disclosed in Research Disclosure, Vol. 367, November 1994, Item 36736.
In a specific, preferred form it is contemplated to employ as a dopant a hexacoordination complex satisfying the formula:
[ML6 ]n (IV)
where
M is filled frontier orbital polyvalent metal ion, preferably Fe+2, Ru+2, Os+2, Co+3, Rh+3, Ir+3, Pd+4 or Pt+4 ;
L6 represents six coordination complex ligands which can be independently selected, provided that least four of the ligands are anionic ligands and at least one (preferably at least 3 and optimally at least 4) of the ligands is more electronegative than any halide ligand; and
n is -2, -3 or -4.
The following are specific illustrations of dopants capable of providing shallow electron traps:
| ______________________________________ |
| SET-1 [Fe(CN)5 ]-4 |
| SET-2 [Ru(CN)5 ]-4 |
| SET-3 [Os(CN)5 ]-4 |
| SET-4 [Rh(CN)5 ]-3 |
| SET-5 [Ir(CN)5 ]-3 |
| SET-6 [Fe(pyrazine)(CN)5 ]-4 |
| SET-7 [RuCl(CN)5 ]-4 |
| SET-8 [CsBr(CN)5 ]-4 |
| SET-9 [RhF(CN)5 ]-3 |
| SET-10 [IrBr(CN)5 ]-3 |
| SET-11 [FeCO(CN)5 ]-3 |
| SET-12 [RUF2 (CN)4 ]-4 |
| SET-13 [OsCl2 (CN)4 ]-4 |
| SET-14 [RhI2 (CN)4 ]-3 |
| SET-15 [IrBr2 (CN)4 ]-3 |
| SET-16 [Ru(CN)5 (OCN)]-4 |
| SET-17 [Ru(CN)5 (N3)]-4 |
| SET-18 [Os(CN)5 (SCN)]-4 |
| SET-19 [Rh(CN)5 (SeCN)]-3 |
| SET-20 [Ir(CN)5 (HOH)]-2 |
| SET-21 [Fe(CN)3 Cl3 ]-3 |
| SET-22 [Ru(CO)2 (CN)4 ]-1 |
| SET-23 [Os(CN)Cl5 ]-4 |
| SET-24 [Co(CN)5 ]-3 |
| SET-25 [IrCl4 (oxalate)]-4 |
| SET-26 [In(NCS)5 ]-3 |
| SET-27 [Ga(NCS)5 ]-3 |
| ______________________________________ |
It is additionally contemplated to employ oligomeric coordination complexes to increase speed, as taught by Evans et al U.S. Pat. No. 5,024,931, the disclosure of which is here incorporated by reference.
The SET dopants are effective in conventional concentrations, where concentrations are based on the total silver in both the silver in the tabular grains and the silver in the second epitaxial phase. Generally shallow electron trap forming dopants are contemplated to be incorporated in concentrations of at least 1×10-7 mole per silver mole up to their solubility limit, typically up to about 5×10-4 mole per silver mole. Preferred concentrations are in the range of from about 10-5 to 10-4 mole per silver mole.
The contrast of the photographic emulsions of the invention can be further increased by doping FCCRS crystal lattice portions of composite tabular grains with a hexacoordination complex containing a nitrosyl or thionitrosyl ligand. Preferred coordination complexes of this type are represented by the formula:
[TE4 (NZ)E']r (V)
where
T is a transition metal;
E is a bridging ligand;
E' is E or NZ;
r is zero, -1, -2 or -3; and
Z is oxygen or sulfur.
The E ligands are typically halide, but can take any of the forms found in the SET dopants discussed above. A listing of suitable coordination complexes satisfying formula V is found in McDugle et al U.S. Pat. No. 4,933,272, the disclosure of which is here incorporated by reference.
The contrast increasing dopants (hereinafter also referred to as NZ dopants) can be incorporated in the composite tabular grain structure at any convenient location. However, if the NZ dopant is present at the surface of the grain, it can reduce the sensitivity of the grains. It is therefore preferred that the NZ dopants be located in the tabular host portions so that they are separated from the grain surface. Preferred contrast enhancing concentrations of the NZ dopants range from 1×10-11 to 4×10-8 mole per silver mole, with specifically preferred concentrations being in the range from 10-10 to 10-8 mole per silver mole, based on silver in the host grains. It is also possible to locate an NZ dopant in the second epitaxial phase, but this is not a preferred location for this dopant.
A significant advantage of the composite tabular grain structure is that all conventional sensitizations for FCCRS crystal lattice structures are fully applicable to the composite tabular grain emulsions of the invention. Conventional chemical sensitizations are summarized in Research Disclosure, Vol. 365, September 1994, Item 36544, IV. Chemical sensitization. The shell structure insures that all of the exterior surface of the grains is available for sensitization and that difficulties in the sensitization of high iodide silver halides at their surface are avoided. Reduction sensitizers, middle chalcogen (e.g., sulfur) sensitizers, and noble metal (e.g., gold) sensitizers, employed singly or in combination are specifically contemplated.
The emulsions of the invention can be reduction sensitized in any convenient conventional manner. Conventional reduction sensitizations are summarized in Research Disclosure, Item 36544, cited above, IV. Chemical sensitization, paragraph (1). A specifically preferred class of reduction sensitizers are the 2-[N-(2-alkynyl)amino]-meta-chalcazoles disclosed by Lok et al U.S. Pat. Nos. 4,378,426 and 4,451,557, the disclosures of which are here incorporated by reference.
Preferred 2-[N-(2-alkynyl)amino]-meta-chalcazoles can be represented by the formula:
(VI) ##STR3## where X=O, S, Se;
R1 =(VIa) hydrogen or (VIb) alkyl or substituted alkyl or aryl or substituted aryl; and
Y1 and Y2 individually represent hydrogen, alkyl groups or an aromatic nucleus or together represent the atoms necessary to complete an aromatic or alicyclic ring containing atoms selected from among carbon, oxygen, selenium, and nitrogen atoms.
As disclosed by Eikenberry et al, cited above, the formula (VI) compounds are generally effective (with the (VIb) form giving very large speed gains and exceptional latent image stability) when present during the heating step (finish) that results in chemical sensitization.
In a preferred form of the invention, an alkynylamino substituent is attached to a benzoxazole, benzothiazole or benzoselenazole nucleus. In one specific preferred form, the compounds VIa of the present invention and companion non-invention compounds VIb can be represented by the following formula:
(VII) ##STR4## where ##STR5##
Other preferred VIb structures have R1 as ethyl, propyl, p-methoxyphenyl, p-tolyl, or p-chlorophenyl with R2 or R3 as halogen, methoxy, alkyl or aryl.
Whereas previous work employing compounds with structure similar to VIa and VIb described speed gains of about 40% using 0.10 mmole/silver mole when added after sensitization and prior to forming the layer containing the emulsion (Lok et al U.S. Pat. No. 4,451,557), speed gains have been demonstrated by Eikenberry et al ranging from 66% to over 250% , depending on the emulsion and sensitizing dye utilized, by adding 0.02-0.03 mmole/silver mole of Vb during the sensitization step. Significantly higher levels of fog are observed when the VIa compounds are employed.
The VIb compounds of the present invention typically contains an R1 that is an alkyl or aryl. It is preferred that the R1 be either a methyl or a phenyl ring for the best increase in speed and latent image keeping.
The compounds of the invention are added to the silver halide emulsion at a point subsequent to precipitation to be present during the finish step of the chemical sensitization process. A preferred concentration range for [N-(2-alkynyl)-amino]-meta-chalcazole incorporation in the emulsion is in the range of from 0.002 to 0.2 (most preferably 0.005 to 0.1) mmole per mole of silver. In a specifically preferred form of the invention [N-(2-alkynyl)amino]-meta-chalcazole reduction sensitization is combined with conventional gold (or platinum metal) and/or middle (S, Se or Te) chalcogen sensitizations. These sensitizations are summarized in Research Disclosure Item 36544, previously cited, IV. Chemical sensitization. The combination of sulfur, gold and [N-(2-alkynyl)amino]-meta-chalcazole reduction sensitization is specifically preferred.
A specifically preferred class of middle chalcogen sensitizers are tetrasubstituted middle chalcogen ureas of the type disclosed by Herz et al U.S. Pat. Nos. 4,749,646 and 4,810,62, the disclosures of which are here incorporated by reference. Preferred compounds include those represented by the formula:
(VIII) ##STR6## wherein X is sulfur, selenium or tellurium;
each of R1, R2, R3 and R4 can independently represent an alkylene, cycloalkylene, alkarylene, aralkylene or heterocyclic arylene group or, taken together with the nitrogen atom to which they are attached, R1 and R2 or R3 and R4 complete a 5 to 7 member heterocyclic ring; and
each of A1, A2, A3 and A4 can independently represent hydrogen or a radical comprising an acidic group,
with the proviso that at least one A1 R1 to A4 R4 contains an acidic group bonded to the urea nitrogen through a carbon chain containing from 1 to 6 carbon atoms.
X is preferably sulfur and A1 R1 to A4 R4 are preferably methyl or carboxymethyl, where the carboxy group can be in the acid or salt form. A specifically preferred tetrasubstituted thiourea sensitizer is 1,3-dicarboxymethyl-1,3-dimethylthiourea.
Specifically preferred gold sensitizers are the gold (I) compounds disclosed by Deaton U.S. Pat. No. 5,049,485, the disclosure of which is here incorporated by reference. These compounds include those represented by the formula:
AuL2+ X- or AuL(L1)+ X- (IX)
wherein
L is a mesoionic compound;
X is an anion; and
L1 is a Lewis acid donor.
As previously disclosed, in preferred photographic applications the tabular grain emulsions of the invention are spectrally sensitized. One of the significant advantages of the invention is that the presence of a high iodide first epitaxial phase on the major faces of the tabular grains can improve the adsorption of the spectral sensitizing dye or dyes employed and, particularly when the oxidation potential of the dye is more negative than the threshold value stated above, increase the efficiency with which photon energy is transferred between the spectral sensitizing dye and the grains.
Any conventional spectral sensitizing dye or dye combination can be employed with the emulsions of the invention. Suitable spectral sensitizing dye selections are disclosed in Research Disclosure , Item 36544, cited above, Section V. Spectral sensitization and desensitization. Preferred spectral sensitizing dyes are polymethine dyes, including cyanine, merocyanine, complex cyanine and merocyanine (i.e., tri-, tetra- and polynuclear cyanine and merocyanine), oxonol, hemioxonol, styryl, merostyryl, streptocyanine, hemicyanine and arylidene dyes. Specifically preferred blue sensitizing dyes are those disclosed by Kofron et al U.S. Pat. No. 4,439,520. The supersensitizing dye combinations set out in Research Disclosure Item 36544, Section V, A. Sensitizing dyes, paragraphs (6) and (6a) are specifically contemplated.
The following are illustrations of specific spectral sensitizing dyes contemplated for use with the emulsions of the invention, together with their oxidation (Eox) and reduction (Ered) potentials in volts:
Anhydro-3,3'-bis(3-sulfopropyl)naphtho[1,2-d]thiazolothiacyanine hydroxide, triethylammonium salt Eox=1,300 Ered=-1,359
Anhydro-3,3'-bis(3-sulfopropyl)-4'-phenylnaphtho[1,2-d]thiazolothiazolinocy anine hydroxide, sodium salt Eox=1.085 Ered=-1.758
Anhydro-5'-chloro-3,3'-bis(3-sulfopropyl)naphtho[1,2-d]oxazolothiacyanine hydroxide, triethylammonium salt Eox=1.375 Ered=-1.437
Anhydro-3,3'-bis(3-sulfopropyl)-4,5,4',5'-dibenzothiacyanine hydroxide, sodium salt Eox=1.213 Ered =-1.371
SS-5
Anhydro-3,3'-bis(3-sulfopropyl)-5,6-dimethoxy-4'-phenylthiacyanine hydroxide, sodium salt Eox=1.240 Ered=-1.401
Anhydro-5-chloro-3'-ethyl-3-(4-sulfobutyl)thiacyanine, inner salt Eox=1.399 Ered=-1.269
Anhydro-5,5'-dimethoxy-3,3'-bis(3-sulfopropyl)thiacyanine hydroxide, inner salt Eox=1.310 Ered =-1.361
Anhydro-5-chloro-3,3'-bis(3-sulfopropyl)thiacyanine hydroxide, sodium salt Eox=1.418 Ered=-1.309
Anhydro-5,5'-bis(methylthio)-3,3'-bis(3-sulfobutyl)thiacyanine hydroxide, triethylammonium salt Eox=1.367 Ered=-1.249
Anhydro-5,6-dimethoxy-5'-phenyl-3,3'-bis(3-sulfopropyl)thiacyanine hydroxide, triethylammonium salt Eox=1.240 Ered=-1.417
Anhydro-3'-(2-carboxy-2-sulfoethyl)-l-ethyl-5',6'-dimethoxynaphtho[1,2-d]th iazolothiocyanine hydroxide, potassium salt Eox=1.153 Ered=-1.462
Anhydro-3,3'-bis(3-sulfopropyl)-5',6'-dimethoxy-5-phenyloxathiacarbocyanine hydroxide, sodium salt Eox=1.259 Ered=-1.593
3'-Ethyl-3-methyl-6-nitrothiathiazolinocyanined iodide Eox=1.271 Ered=-1.774
Anhydro-5'-chloro-5-phenyl-3,3'-bis(3-sulfopropyl)oxathiacyanine hydroxide, triethylammonium salt Eox=1.447 Ered=-1.580
Anhydro-5'-fluoro-3,3'-bis(3-sulfopropyl)naphtho[1,2-d]thiazolothiacyanine hydroxide, triethylammonium salt Eox=1.322 Ered=-1.318
Anhydro-5-chloro-3,3'-bis(sulfopropyl)naphtho[1,2-d]thiazolothiacyanine hydroxide, triethylammonium salt Eox=1.341 Ered=-1.273
Anhydro-4',5'-benzo-3,3'-bis(3-sulfopropyl)-5-pyrrolooxathiacyanine hydroxide, triethylammonium salt Eox=1.334 Ered=-1.453
Anhydro-4',5'-benzo-3,3'-bis(3-sulfopropyl)-5-phenyloxathiacyanine hydroxide, triethylammonium salt Eox =1.319 Ered=-1.484
Anhydro-5,5'-dichloro-3,3'-bis(2-sulfoethyl)thiacyanine hydroxide, triethylammonium salt Eox=1.469 Ered=-1.206
Anhydro-4',5'-benzo-5-methoxy-3,3'-bis(3-sulfopropyl)oxathiacyanine hydroxide, sodium salt Eox=1.283 Ered=-1.530
Anhydro-5-cyano-3,3'-bis(3-sulfopropyl)-5'-phenylthiacyanine hydroxide, triethylammonium salt Eox=1.445 Ered=-1.234
Anhydro-5'-chloro-5-pyrrolo-3,3'-bis(3-sulfopropyl)oxathiacyanine hydroxide, triethylammonium salt Eox=1.461 Ered=-1.380
Anhydro-5,5'-dichloro-3,3'-bis(3-sulfopropyl)thiacyanine hydroxide, triethylammonium salt Eox=1.469 Ered=-1.215
Anhydro-5,5'-diphenyl-3,3'-bis(3-sulfopropyl)thiacyanine hydroxide, triethylammonium salt Eox=1.387 Ered=-1.287
Anhydro-5-chloro-5'-phenyl-3,3'-bis(3-sulfopropyl)thiacyanine hydroxide, triethylammonium salt Eox=1.428 Ered=-1.251
Anhydro-5-chloro-5'-pyrrolo-3,3'-bis(3-sulfopropyl)thiacyanine hydroxide, triethylammonium salt Eox=1.442 Ered=-1.212
In addition to the features specifically described, it is recognized that the emulsions can contain any convenient conventional selection of additional features. For example, the features of the emulsions, such as vehicle (including peptizers and binders), hardeners, antifoggants and stabilizers, blended grain populations, coating physical property modifying addenda (coating aids, plasticizers, lubricants, antistats, matting agents, etc.), and dye image formers and modifiers can take any of the forms described in Research Disclosure, Item 36544, cited above. Selections of these other emulsion features are preferably undertaken as taught in the patents cited above to describe the starting tabular grain emulsions.
The invention can be better appreciated by reference to the following specific examples. The term "oxidized gelatin" is employed to indicate gelatin that has been treated with hydrogen peroxide to reduce its methionine content below detectable levels. pH was lowered by using nitric acid and increased by using sodium hydroxide.
PAC Host Tabular Grain Emulsion HT-1A silver bromide host tabular grain emulsion was prepared by charging a reaction vessel with 1.25 g/L of oxidized gelatin, 1.115 g/L NaBr, 0.1 g/L of block copolymer A, and 6 L of distilled water.
HO--[(CH3)CHCH2 O]x --(CH2 CH2 O)y --[CH2 CH(CH3)O]x',--H
x=x'=25; y=7
The contents of the reaction vessel were adjusted to a pH of 1.78 at 40°C Nucleation occurred during a one minute period during which 0.8 m/L of AgNO3 and 0.84 m/L NaBr were added at the rate of 50 mL/min. The temperature of the reaction vessel was ramped to 60°C after the addition of 0.0892 mole of NaBr. Ammonia was then generated in situ by the addition of 0.115 mole of ammonium sulfate and 0.325 mole of sodium hydroxide. Ammoniacal digestion was undertaken for 9 minutes, after which time the digestion was quenched by the addition of 0.2265 mole of nitric acid. Additional gelatin, 99.84 g of oxidized gelatin, and surfactant, block copolymer A (1.0 mL) were introduced into the reaction vessel.
A first growth segment (I) then occurred over a period of 20 minutes at a pH of 5.85 , pBr of 2.2, 60°C, by introducing NaBr and AgNO3 solutions employed for grain nucleation at the rates of 9.2 and 9.0 mL/min, respectively. A second growth segment (II) took place over 64 minutes by continuing precipitation as described for growth segment I, except that 1.6 mol/L AgNO3 was ramped from 9 to 80 mL/min and 1.679 m/L NaBr was ramped from 9.1 to 78.5 mL/min. A final growth segment was conducted for 19 minutes at the terminal flow rate of growth segment II.
The emulsion was then cooled to 40°C and adjusted to a pBr of 3.6 during ultrafiltration. The pH of the emulsion was adjusted to 5.9.
The resulting silver bromide tabular grain emulsion was monodispersed, having a COV of less than 30 percent. The average ECD of the emulsion grains was 1.44 μm, and the average thickness of the grains was 0.10 μm. The average aspect ratio of the tabular grains 14.4. Greater than 90 percent of total grain projected area was accounted for by tabular grains.
A reaction vessel was charged with 1 mole of Emulsion HT-1. The temperature of the reaction vessel was adjusted to 60°C, and its pBr was brought to 4.0 by the slow addition of AgNO3. The silver content of the grains was increased by 18 percent, based on total silver, by the double jet precipitation of AgI over 10 minutes by adding AgNO3 and KI each at a flow rate of 35 mL/min. while monitoring the pI of the reaction vessel to control host grain metathesis. At the conclusion of precipitation the pI of the reaction vessel was adjusted to 7.1 with KI and the pH was adjusted to 5.6.
Microscopic analysis of the resulting emulsion revealed that in excess of 90 percent of total grain projected area was accounted for by composite tabular grains containing high iodide silver halide plates on their major faces and edges. Greater than 40 percent of the tabular grain major faces were covered by the high iodide plates. Scanned probe microscopy revealed that the plates varied from 4 to 6 nm in thickness. The plates were observed to contain βphase silver iodide, but the presence of γ phase silver iodide could not be excluded. Analytical electron microscopy observations were consistent with the plates having a high (>90 mole %) iodide content. A measured lattice constant of 6.5 Å was observed, compared to a known lattice constant of 6.496 Å for AgI. Some evidence of host grain metathesis was observed, and a nontabular AgI grain population was also present.
The emulsion was coated at 10.76 mg/dm2 silver with an equal amount of gelatin on a cellulose acetate photographic support with an anithalation backing layer. The emulsion layer was overcoated with 21.53 mg/dm2 of gelatin containing 1.5 percent by weight, based on total gelatin, of bis(vinylsulfonyl)methane hardener. A second, identical coating was prepared, except that the antihalation backing was omitted. Third and fourth coatings identical to the first and second coatings were prepared, except that Emulsion HT-1 was substituted for Emulsion CT-1.
From reflection and transmission analysis the absorptions of Emulsions HT-1 and CT-1 as a function of wavelength were determined and are represented as shown in FIG. 3. Emulsion CT-1 demonstrated a significantly higher absorption that Emulsion HT-1 up to wavelengths approaching 500 nm. Peak absorption of Emulsion HT-1 was observed at 423 nm. Multiplying the spectral output of a 5500° K. Daylight V light source by the absorptions of FIG. 3 over the wavelength region of 360 to 700 nm gives an integrated light absorption of 175×1010 photons/cm2 /sec for Emulsion HT-1 and 745×1010 photons/cm2 /sec for Emulsion CT-1. This demonstrates somewhat more than 4 times greater photon absorption for Emulsion CT-1 as compared to Emulsion HT-1.
PAC Host Tabular Grain Emulsion HT-2A silver iodobromide host tabular grain emulsion was prepared by charging a reaction vessel with 2 g/L of gelatin (Rousselot™), 6 g/L NaBr, 0.65 mL of block copolymer A, and 4956 mL of distilled water. The contents of the reaction vessel were adjusted to a pH of 6.0 at 40°C at a pBr of 1.35. The temperature of the reaction vessel was then raised to 70° C. Nucleation occurred during a three minute period during which 0.393 m/L of AgNO3 at a rate of 87.6 mL/min and 2 m/L NaBr at a rate of 20 mL/min were added. An ammonia digest was initiated by adding 0.27 mole of NH4 OH. Ammoniacal digestion was undertaken for 1.5 minutes, after which time the digestion was quenched by the addition of 0.37 mole of nitric acid.
Distilled water in the amount of 1820 mL containing 77 g/L of gelatin with 0.25 mL of block copolymer A was added to the reaction vessel. A first growth segment (I) was then conducted over 3.0 minutes by introducing 87.6 mL/min of the 0.393 m/L AgNO3 and 13.2 mL/min of the 2 m/L NaBr while maintaining a pBr of 1.55. A second growth segment (II) was conducted over 25 minutes by adding 2.75 m/L AgNO3 and 2.7085 m/L NaBr containing 0.04125 m/L KI, each at accelerating flow rates ranging from 15 to 40 mL/min. A third growth segment (III) was a continuation of the preceding growth segment, lasting 31 minutes with addition of the same solutions being accelerated from 40 to 102 mL/min. NaBr in the amount of 1.925 moles in 665 g of distilled water were then added followed by the dump addition of 0.36 mole of AgI Lippmann. AgNO3 at 2.75 m/L and 2 m/L NaBr were then each run into the reaction vessel at a constant rate of 50 mL/min until the pBr of the reaction vessel reached 2.4 (approximately 24 minutes).
The emulsion was washed at 40°C to a pBr of 3.6 by ultrafiltration. The pH of the emulsion was adjusted to 5.6.
The emulsion was a run-dump silver iodobromide tabular grain emulsion. The grains contained 1.5 mole % I added during the run and 3 mole % I added in the dump following precipitation of 69 percent of total silver.
The resulting silver iodobromide tabular grain emulsion was monodispersed, having a COV of less than 30 percent. The average ECD of the emulsion grains was 3.25 μm, and the average thickness of the grains was 0.13 μm. The average aspect ratio of the tabular grains 25. Greater than 70 percent of total grain projected area was accounted for by tabular grains.
Formation of this emulsion followed the description provided above for the preparation of Emulsion CT-1, except as noted. Emulsion HT-2 was substituted for Emulsion HT-1. The temperature of the reaction vessel was 60°C AgNO3 and KI were added in two 10 minute growth segments. In the first segment the AgNO3 addition was accelerated from 3.5 to 17.5 mL/min while KI addition was accelerated from 5 to 25 mL/min. In the second segment the AgNO3 addition was accelerated from 17.5 to 35 mL/min while KI addition was accelerated from 25 to 50 mL/min. The additional AgI precipitated accounted for 20.6 percent of total silver forming the composite grains.
Microscopic analysis of the resulting emulsion revealed that in excess of 95 percent of total grain projected area was accounted for by composite tabular grains containing triangular and hexagonal high iodide silver halide plates on their major faces and edges. Greater than 55 percent of the tabular grain major faces were covered by the high iodide plates. Scanned probe microscopy revealed that the plates varied from 15 to 30 nm in thickness. Plates were also observed on the edges of the host tabular grains. A plan view of a typical grain is shown in FIG. 4, and a section view of typical grains is shown in FIG. 5.
Iodide analysis revealed three distinct phases--the run iodide, the dump iodide and the iodide in the plates. The lattice constant of the crystal lattice of the plates was 6.4, indicating a high (>90 mole %) iodide phase, probably containing a small fraction of bromide ion.
The light absorption analysis of Example 1 was repeated using Emulsions HT-2 and CT-2, except additional samples of these emulsions were examined with the blue spectral sensitizing dye SS-23 added at concentrations of 600 mg/Ag mole.
From reflection and transmission analysis the absorptions of dyed and undyed samples Emulsions HT-2 and CT-2 as a function of wavelength were determined and are represented as shown in FIG. 6. Emulsion HT-2 without dye is shown as curve HT-2-D. It exhibits the least absorption in the blue region of the spectrum. Emulsion HT-2 with dye is shown as curve HT-2+D shows increased blue absorption, attributable to the spectral sensitizing dye, with peak absorption occurring in the long blue portion of the spectrum. Emulsion CT-2 without dye, shown as Curve CT-2-D, shows blue absorption superior to that of HT-2-D and shows short blue absorption superior to that of HT-2+D. Emulsion CT-2 with dye, shown as Curve CT-2+D, shows superior overall blue absorption as compared with the remaining emulsion samples.
Multiplying the spectral output of a 5500° K. Daylight V light source by the absorptions of FIG. 6 over the wavelength region of 360 to 700 nm gives the integrated light absorptions shown in Table II.
| TABLE II |
| ______________________________________ |
| Emulsion Integrated Light |
| Sample Absorption photons/sec/cm2 |
| ______________________________________ |
| HT - 2 - D 294 × 1010 |
| CT - 2 - D 729 × 1010 |
| HT - 2 + D 630 × 1010 |
| CT - 2 + D 959 × 1010 |
| ______________________________________ |
This demonstrates the superior blue light absorption that are available by employing the emulsions of the invention.
PAC Composite Tabular Grain Emulsion CT-3Starting with HT-2, but with the pBr of the emulsion adjusted to 5.06, the preparation procedure for CT-2 was repeated, but with these differences: The second growth segment in which AgNO3 and KI were added was reduced to 6.1 minutes. In the first growth segment KI addition was accelerated from 4 to 10 mL/min and in the second growth segment KI addition was accelerated from 10 to 16.1 mL/min. The AgNO3 flow in the second growth segment ended at 28.2 mL/min. The total AgI precipitated accounted for 9.2 percent of total silver forming the composite grains.
A plane view of a typical grain is shown in FIG. 7, and a section view of typical grains is shown in FIG. 8. Compared to Emulsion CT-2, there were fewer high iodide plates at the edges of the host tabular grains. Also, instead of being discrete with triangular or hexagonal boundaries, the plates appeared to coalesce with adjacent plates, leaving no discernible boundaries between adjacent plates.
PAC Host Tabular Grain Emulsion HT-4A silver iodobromide host tabular grain emulsion was prepared by charging a reaction vessel with 0.80 g/L of oxidized gelatin, 0.851 g/L NaBr, 0.7 g/L of block copolymer B, and 6 L of distilled water.
HO--(CH2 CH2 O)y --[(CH3)CHCH2 O]x --(CH2 CH2 O)y,--H
x=22; y=y'=6
The contents of the reaction vessel were adjusted to a pH of 1.78 at 45°C Nucleation occurred during a one minute period during which 0.5 m/L of AgNO3 and 0.54 m/L NaBr were added at the rate of 58 mL/min. The temperature of the reaction vessel was ramped to 60°C after the addition of 0.098 mole of NaBr. Ammonia was then generated insitu by the addition of 0.077 mole of ammonium sulfate and 0.241 mole of sodium hydroxide. Ammoniacal digestion was undertaken for 9 minutes, after which time the digestion was quenched by the addition of 0.21 mole of nitric acid. Additional gelatin (150.0 g of oxidized gelatin), NaBr (0.123 mole), and block copolymer B (1.4 mL) were introduced into the reaction vessel.
A first growth segment (I) then occurred over a period of 20 minutes at a pH of 5.5, pBr of 1.6, 60°C, by introducing NaBr and AgNO3 solutions employed for grain nucleation at the rates of 15 and 16.7 mL/min, respectively. A second growth segment (II) took place over 75 minutes by continuing precipitation as described for growth segment I, except that 1.6 mol/L AgNO3 was ramped from 9 to 69 mL/min and 1.622 m/L NaBr plus 0.0676 KI was ramped from 9.6 to 69 mL/min. A third growth segment (III) occurred for 8.5 minutes at the final addition rate of the second growth segment. A final growth segment was conducted for 20 minutes at the flow rate of growth segment III, except that 1.69 m/L NaBr was substituted for NaBr plus KI for the purpose of reducing the iodide concentration at the surface of the tabular grains during the precipitation of the final 20 percent of silver deposition.
The emulsion was then cooled to 40°C and adjusted to a pBr of 3.5 during ultrafiltration. The pH of the emulsion was adjusted to 5.5.
The resulting silver iodobromide tabular grain emulsion was monodispersed, having a COV of less than 30 percent. The average ECD of the emulsion grains was 2.87 μm, and the average thickness of the grains was 0.098 μm. The average aspect ratio of the tabular grains was 29.3. Greater than 90 percent of total grain projected area was accounted for by tabular grains.
A one mole sample of Emulsion HT-4 was partially shelled by depositing silver iodobromide (36 mole % I) as a shell over the exterior of the host tabular grains. A total of 0.225 mole of AgBr0.64 I0.36 was deposited over 38.5 minutes by the double jet addition of AgNO3 as a silver salt solution and a mixture of NaBr and KI as a mixed halide salt solution. Shell precipitation was conducted at 65°C and a pBr of 3.6 . A total of 0.0918 mole of silver iodide was precipitated in the shell.
Microscopic examination of the grains revealed that the shell covered all visible exterior edge faces of the host tabular grains and 40 percent of the total exterior surface. Shell growth began at the edges of the grains, entirely covering the edges, and then progressed inwardly as precipitation continued, entirely covering all areas of the major faces closer to the edges than the boundaries of the partial shell nearest the centers of the major faces.
The shelling procedure of Emulsion ST-4 was modified to eliminate the bromide added with the iodide. This resulted in the precipitation of 0.0919 mole of silver iodide onto the host tabular grain emulsion HT-4.
Microscopic analysis of the resulting emulsion revealed that in excess of 90 percent of total grain projected area was accounted for by composite tabular grains containing high iodide silver halide plates on their major faces and edges. Greater than 15 percent of the tabular grain major faces were covered by the high iodide plates.
The light absorption analysis of Example 2 was repeated using Emulsions HT-4, ST-4 and CT-4, but with 800 g of blue spectral sensitizing dye SS-23 per silver mole adsorbed.
The absorption performance of dyed samples is shown in FIG. 9. All of the dyed samples demonstrated similar absorption in the long (450 to 500 nm) blue region of the spectrum; but in the short (400 to 450 nm) blue region of the spectrum, a clear separation on absorptions was observed. Minimum short blue absorption was demonstrated by Emulsion HT-4 with dye (HT-4+D). When iodide was increased by creating a silver iodobromide shell, a clear increase in blue absorption was observed for Emulsion ST-4 plus dye (ST-4+D). However, the short blue absorption of ST-4+D was limited by the limited ability to incorporate iodide into the face centered cubic rock salt crystal lattice structure forming the shell. The superiority of forming a high iodide phase on the major faces of the host tabular grains is shown by the dyed sample of Emulsion CT-4 (CT-4+D).
Multiplying the spectral output of a 5500° K. Daylight V light source by the absorptions of samples of Emulsions HT-4, ST-4 and CT-4, with (+D) and without (-D) dye, over the wavelength region of 360 to 700 nm gives the integrated light absorptions shown in Table III.
| TABLE III |
| ______________________________________ |
| Emulsion Integrated Light |
| Sample Absorption photons/sec/cm2 |
| ______________________________________ |
| HT - 4 - D 224 × 1010 |
| ST - 4 - D 369 × 1010 |
| CT - 4 - D 498 × 1010 |
| HT - 4 + D 807 × 1010 |
| ST - 4 + D 849 × 1010 |
| CT - 4 + D 995 × 1010 |
| ______________________________________ |
This demonstrates the superior blue light absorption that is available by employing the emulsions of the invention. It further demonstrates that similar levels of light absorption can not be realized by adding the same amount of iodide as in the emulsions of the invention, but in a surface silver iodobromide shell. Even though CT-4 contained a high iodide phase covering only a minimal 15 percent of its major faces, it compared favorably to ST-4 that contained a silver iodobromide phase of the same overall iodide content distributed over 40 percent of its major faces.
PAC Host Tabular Grain Emulsion HT-5A silver iodobromide (3 mole % I) tabular grain emulsion was precipitated in the following manner: A reaction vessel was charged with 0.667 g/L gelatin, 1.25 g/L NaBr and 6.3 L of distilled water at 70°C The contents of the reaction vessel were brought to a pH of 3.5 with nitric acid. Nucleation occurred over a 10 sec period by the double jet addition of 1.4 M AgNO3 at 75 mL/min and a salt at the same flow rate containing 1.386M NaBr and 0.014M KI. The contents of the reaction vessel were held for 6 minutes and then the temperature was ramped to 80° C. over a period of 7 minutes. Then 1.5 L of a solution containing 20 g/L of gelatin were added, and pH was adjusted to 4.5 with NaOH. Six growth segments (I-VI) defining the remainder of the precipitation were conducted at 80°C, a pH 4.5 and a pBr of 1.78 using 2.5M AgNO3 and 2.425M NaBr containing 0.075M KI.
Growth I took 4.5 min with silver flowing at 15.7 mL/min and the salts at 23.6 mL/min. Growth II extended for 9 minutes during which time the silver flow rate was ramped from 15.7 to 27.3 mL/min, and the flow rate of the salts was ramped from 16.7 to 28.4 mL/min. Growth III was the same time as growth II, except that the respective flow rate ramps were 27.3 to 40.9 and 28.4 to 42.5 mL/min. Growth IV extended over 13.5 minutes with the respective flow rate ramps of 40.9 to 66.1 and 42.5 to 68 mL/min. Growth V took the same time as Growth IV with the respective flow rate ramps of 66.1 to 97.2 and 68 to 99.8 mL/min. Growth VI was 18 minutes long, and the respective flow rate ramps were 97.2 to 120.7 and 99.8 to 123.8 mL/min.
The emulsion was cooled to 40°C and adjusted to a pBr of 3.6 during ultrafiltration. The pH of the emulsion was adjusted to 5.9. The resulting silver iodobromide tabular grain emulsion had a COV of less than 36 percent. The average ECD of the emulsion grains was 2.48 μm, and the average thickness of the grains was 0.10 6 μm. The average aspect ratio of the tabular grains was 23.4. Greater than 90 percent of the total grain projected area was accounted for by tabular grains.
Shelled tabular grain control ST-5 was precipitated similarly as ST-4 only using HT-5 as the substrate and at a pBr of 5.06 rather than 3.6.
The shelled grains exhibited an average ECD of 2.81 μm and an average grain thickness of 0.137 μm. Average aspect ratio was 20.1. The iodide concentration of the shell was 38 mole percent, raising the overall iodide concentration of the shelled grains to 10.0 mole percent.
This emulsion was prepared similarly to composite tabular grain emulsion CT-4, except that host tabular grain emulsion HT-5 was employed as a substrate and precipitation was conducted at a pBr of 5.06 rather than 3.6.
The composite tabular grains exhibited an average ECD of 2.88 μm and an average grain thickness of 0.116 μm. Average aspect ratio was 24.8. The overall iodide concentration of the composite grains was 9.9 mole percent.
Prior to chemical sensitization, both ST-5 and CT-5 were adjusted to a pBr of 4.37 and epitaxially deposited with 8.0 mole % AgCl using SS-1 at 431.4 mg/Ag mole as a dye director as taught by Maskasky, U.S. Pat. No. 4,459,353. Subsequently chemical sensitization was effected by the sequential addition of 60 mg/Ag mole of NaSCN, 4 mg/Ag mole of N,N'-dicarboxymethyl-N,N'-dimethylthiourea, 2 mg/Ag mole of Au(I) bis(trimethylthiotriazole), and 2.5 mg/Ag mole of 3-methyl-1,3-benzothiazolium iodide to the emulsion melt followed by a 5 min. temperature hold at 50°C At the conclusion finish of the heat cycle, 115 mg/Ag mole of 1-(3-acetamidophenyl)-5-mercaptotetrazole (APMT) were added to the melt.
Film coatings were made on a cellulose acetate photographic film support with an antihalation backing layer. ST-5 and CT-5 were doctored with 1.750 gm/Ag mole of 4-hydroxy-6-methyl-1,3,3a,7-tetra-azaindene and coated at the following coating coverages: silver halide 10.76 mg/dm2, gelatin 32.28 mg/dm2, and 9.684 mg/dm2 of the yellow dye-forming coupler YC-1. The emulsion layer was overcoated with 8.610 mg/dm2 gelatin, to which 1.5 percent by weight, based on total coated gelatin, bis(vinylsulfonyl)methane hardener was added. ##STR7##
The coated emulsions were Given a sensitometric exposure for 1/50" through a 0-3 step chart from to 500 nm in 10 nm increments and then processed in the motion picture film process ECN-2 described in Kodak Publication H-24, Manual for Processing Eastman Color Films.
The relative speeds reported in Table IV below were based on the reciprocals of the lux-second/cm2 required to give a density 0.2 unit above Dmin.
| TABLE IV |
| ______________________________________ |
| 430 nm (peak AgI absorption) |
| 480 nm (peak dye absorption) |
| Relative |
| Relative |
| Emulsion |
| Dmin Gamma Speed Speed |
| ______________________________________ |
| ST-5 0.36 0.13 100 100 |
| CT-5 0.17 0.67 2230 2200 |
| ______________________________________ |
It can be readily appreciated that the tabular grain emulsion of the present invention is, by reason of the high iodide epitaxial phase partially covering the major faces of the tabular, superior to a comparable tabular grain emulsion, but with an iodide saturated silver iodobromide shell substituted for the high iodide epitaxial phase. The advantage is observed in both the long and short blue regions of the spectrum.
This example demonstrates that higher levels of photographic performance are realized when the spectral sensitizing dye employed has a reduction potential more negative than -1.30 volts. A high chloride second epitaxial phase was employed for chemical sensitization.
A silver iodobromide host tabular grain emulsion was prepared by charging a reaction vessel with 2.083 g/L of gelatin (Rousellot™), 6.25 g/L NaBr, 0.271 g/L of the surfactant Emerest 2648™, a dioleate ester of polyethylene glycol (mol. wt. 400) (S6), and 6 L of distilled water. The contents of the reaction vessel were adjusted to a pH of 6.0 at 40° C. after which the temperature was raised to 75°C Nucleation occurred during a one minute period during which 0.50 m/L of AgNO3 and 2.0 m/L of NaBr were added at a rate of 62.0 mL/min and 22.8 mL/min, respectively. Ammonia was then generated insitu by the addition of 0.0282 mole of ammonium sulfate and 0.086 mole of sodium hydroxide, which brought the reaction vessel to a pH of 10.2. Ammoniacal digestion was undertaken for 1.5 minutes after which time the digestion was quenched by the addition of 0.07 mole of nitric acid. An additional 176.25 g of gelatin (Rousellot™), surfactant S6, and 0.122 mole of NaBr were introduced into the reaction vessel such that the pBr was brought to 1.343 at 75°C The pH was then adjusted to 6.0 with NaOH.
A first growth segment (I) then occurred over a period of 3 minutes at a pH of 6.0, a pBr of 1.34, and a temperature of 75°C by introducing the silver nitrate solution employed for grain nucleation at a rate of 85.3 mL/min and a 2.75 m/L mixed salt solution (1.5% KI, 98.5% NaBr) at a rate of 18.7 mL/min. A second growth segment (II) took place over 25 minutes by continuing precipitation as described for growth segment I, except that 2.75 mol/L AgNO3 was ramped linearly from 18.8 to 50.0 mL/min and the mixed halide salt was ramped linearly from 21.2 to 53.8 mL/min. A third growth segment (III) was undertaken for 31 minutes employing the same reagents as in growth segment II. The flow rates were ramped to 127.5 and 132.2 mL/min, respectively. A fourth growth segment (IV) used these terminal flow rates for an additional 1.5 minutes. A final growth segment (V) employed a single AgNO3 jet for 3.25 minutes to impart a pure bromide character to the last 5% of the emulsion.
The emulsion was then cooled to 40°C and adjusted to a pBr of 3.378 during ultrafiltration. The pH of the emulsion was adjusted to 5.6.
The resulting AgIBr tabular grain emulsion contained 1.5 mole % bulk iodide, based on total silver, and had a COV of 44 percent. The mean ECD of the emulsion grains was 3.29 μm, and the average thickness of the grains was 0.103 μm. The average aspect ratio of the tabular grains was 32. Greater than 90 percent of total grain projected area was accounted for by tabular grains.
A 4 L reaction vessel was charged with one mole of HT-6 and 500 mL of distilled water, allowed to equilibrate at 40°C for 10 minutes and then brought to a temperature of 60°C In a first growth segment I the pBr was then raised from 3.681 to 5.261 during the first 3 minutes of a 13.4 minute segment in which a double jet addition of 0.25N AgNO3 reagent was linearly ramped from 4.1 to 14.1 mL/min while a 0.4M KI solution was linearly ramped from 4.6 to 8.1 mL/min.
A second growth segment II followed lasting 14.3 minutes in which the silver nitrate was ramped from its final value in segment I to a value of 28.1 mL/min while the KI reagent flow rate was accelerated to 26.8 mL/min. This and a following segment were controlled at a pBr of 5.261. A final growth segment III featuring constant flow rates at these terminal values was sufficient to confer an overall additional bulk iodide content of 9.2 mole %, based on total silver forming the composite grains. The iodide present consisted essentially of a pure β phase AgI composition.
A second epitaxial phase was grown onto the corners of the tabular grains contained in samples of emulsions HT-6 and CT-6.
A 800 mL reaction vessel was 0.5 mole of HT-6 or CT-6. Addition of 0.25N AgNO3 was used to raise the pBr from 3.394 to 4.827 at 40°C Sufficient sodium chloride was then added to the reaction vessel to bring its concentration to 4 mole %. The emulsion was then dyed with one of the spectral sensitizing dyes identified below in an amount (0.981 mole) calculated to cover 75% of the emulsion surface area (383.5 m2 /Ag mole). A double jet precipitation of 1.0M AgNO3 and 1.0M NaCl at 22.9 mL/min for 1.75 minutes was sufficient to generate AgCl epitaxial deposits almost exclusively confined to the corners of the tabular grains in an amount totaling 8 mole %, based on total silver. The analyzed composition of these deposits in HT-6 emulsion samples was 65% AgCl, 30% AgBr and 5% AgI.
To each sample receiving the second epitaxial phase as described above were added at 40°C in sequence the following reagents in millimoles per silver mole with 5 minute holds between each successive addition: 1.2335 mmoles of NaSCN, 0.02727 mmole of N,N'-dicarboxymethyl-N,N'-dimethylthiourea, 0.0035 mmole of Au(I) bis(trimethylthiotriazole), and 2.5 mg of 3-methyl-1,3-benzothiazolium iodide. Chemical sensitization was effected by raising the emulsion melt containing addenda to 50°C and holding for 7.5 minutes. Subsequently, the melt was cooled to 40°C, and 0.6453 millimole of 1-(3-acetamidophenyl)-5-mercaptotetrazole (APMT) was introduced. The melt was then prepared for coating.
Single emulsion layer coatings were formulated containing 10.76 mg/dm2 of silver halide, three times that amount of gelatin, and 9.684 mg/dm2 of the yellow dye-forming coupler YC-1. The dye-forming coupler containing emulsion layer was overcoated with 8.608 gm/dm2 of gelatin and hardened with 1.5 percent by weight of bis(vinylsulfonyl)methane.
Coatings were exposed through a 0-4 density step tablet for 1/50" using a Wratten 2B™ filter with a 0.6 density inconel filter and a 3000° K. color temperature (tungsten filament balance) light source. The Wratten 2B filter allowed transmission of light having a wavelength longer than 410 nm. A standard 3.25 min development color negative process (Eastman Color Negative™) was used to develop the latent image.
In Table V the relative log speeds (derived from inertial speeds) of the HT-6 and CT-6 emulsions plus AgCl epitaxy host emulsions sensitized with varied dyes are compared.
| TABLE V |
| ______________________________________ |
| (>410 nm exposures) |
| Dye/ Rel. Log Speed |
| Rel. Log Speed |
| Red. Potential |
| HT-6 + AgCl |
| CT-6 + AgCl |
| (volts) epitaxy epitaxy |
| ______________________________________ |
| SS-22/-1.38 106 121 |
| SS-4/-1.37 125 133 |
| SS-1/-1.36 114 119 |
| SS-21/-1.23 -- 102 |
| SS-23/-1.22 133 100 |
| ______________________________________ |
From Table V it is apparent that the presence of the high iodide plates on the major faces of the host grains increased the speed of the emulsions exposed to light in the wavelength ranges which the dyes were capable of absorbing when spectral sensitizing dyes SS-3, SS-4 and SS-22 were employed. From this it was concluded that when the spectral sensitizing dye has a reduction potential more negative than -1.30 volts (preferably more negative than -1.35 volts) the spectral sensitizing dye is capable of injecting electrons into the high iodide plates on exposure and a higher photographic speed can be expected. In the absence of any spectral sensitizing dye the high iodide plates produce a very large speed advantage, as demonstrated above in Example 5.
This example demonstrates that when a spectral sensitizing dye having a reduction potential more negative than -1.30 (preferably -1.35 ) volts is employed in combination with a compound having a reduction potential more negative than that of the spectral sensitizing dye (preferably having a reduction potential more negative than -1.40 volts) and is limited to a molar concentration of 35 percent or less, based on the compound and the spectral sensitizing dye, a further increase in photographic speed can be realized.
Emulsion CT-6 with AgCl as a second epitaxial phase was prepared, coated and processed as in Example 6, except that a preferred spectral sensitizing dye SS-5 was employed alone or in combination with one of the other dyes shown in Table VI.
| TABLE VI |
| ______________________________________ |
| Spectral Sensitizing |
| Oxidation Potential |
| Reduction Potential |
| Dye (volts) (volts) |
| ______________________________________ |
| SS-23 1.47 -1.22 |
| SS-22 1.46 -1.38 |
| SS-5 1.24 -1.4 |
| SS-2 1.09 -1.76 |
| ______________________________________ |
Dye SS-23 represents a non-preferred spectral sensitizing dye lacking a reduction potential more negative than -1.30 volts. Dyes SS-22 and SS-5 are representative of preferred spectral sensitizing dyes. Dye SS-2 demonstrates a spectral sensitizing dye having a more negative reduction potential than any of the remaining spectral sensitizing dyes.
Integrated light absorptions as well as minimum densities (Dmin), contrast (Gamma) and relative log speeds (Speed) for 365 nm Hg line exposures and 3000° K. exposures are summarized in Table VII. The integrated light absorptions were determined as reported in Examples 1 and 5. The 3000° K. exposures correspond to those described in Example 6. The 365 nm Hg line exposures were conducted through a graduated density step tablet similarly as the 3000° K. exposures, but no filters were employed.
| TABLE VII |
| ______________________________________ |
| Integrated |
| Light |
| 365 Hg Line 3000° K. |
| Absorption |
| Dmin Gamma Dmin Gamma photons/sec/ |
| Dye Speed Speed cm2 |
| ______________________________________ |
| SS-5 0.25 1.02 100 0.27 1.28 100 550.8 × 1010 |
| SS-23(15%) |
| 0.49 0.74 75 0.46 0.74 74 526 × 1010 |
| SS-5(85%) |
| SS-22(35%) |
| 0.24 0.92 98 0.25 0.97 99 334.2 × 1010 |
| SS-5(65%) |
| SS-2(35%) |
| 0.24 0.72 108 0.25 0.81 111 478.6 × 1010 |
| SS-5(65%) |
| ______________________________________ |
From Table VII it is apparent that when spectral sensitizing dye SS-5, which is a representative preferred spectral sensitizing dye having a reduction potential more negative than -1.30 volts, is combined with a minor amount of a spectral sensitizing dye that has a more positive reduction potential, SS-23, the result is a loss in photographic speed. When SS-5 is combined with a minor amount of another preferred spectral sensitizing dye having about the same reduction potential, SS-22, a minimal influence on speed is observed. However, when SS-5 is employed in combination with a minor amount of SS-2, a spectral sensitizing dye having a reduction potential more negative than that of SS-5 and more negative than -1.40 volts, the result is a significant increase in photographic speed.
It should be specifically noted that SS-2 used in combination with SS-5 increased speed, even though overall light absorption was less than that obtained with SS-5 alone. Thus, compounds having more negative reduction potentials than the preferred spectral sensitizing dyes can improve photographic speed, even when displacement of the dye by the compound reduces the level of dye absorption.
Example 7 was repeated, except that the molar ratios of spectral sensitizing dyes SS-5 and SS-2 were varied. In these investigations the sensitizations also differed from those of Example 7 in that 17% less sulfur sensitizer and 12.5% less Gold sensitizer were employed while an additional 0.250 mole of spectral sensitizing dye or dyes was added after the step of holding for 7.5 minutes at 50°C
The results are summarized in Table VIII.
| TABLE VIII |
| ______________________________________ |
| Integrated |
| Light |
| 365 Hg Line 3000° K. |
| Absorption |
| Dmin Gamma Dmin Gamma photons/sec/ |
| Dye Speed Speed cm2 |
| ______________________________________ |
| SS-5 0.17 0.99 100 0.17 1.01 100 572.8 × 1010 |
| SS-2 0.32 0.54 88 0.30 0.57 71 414 × 1010 |
| SS-5(95%) |
| 0.16 1.01 102 0.16 0.98 102 562.3 × 1010 |
| SS-2(5%) |
| SS-5(85%) |
| 0.15 0.90 109 0.16 0.89 107 535.8 × 1010 |
| SS-2(15%) |
| SS-5(75%) |
| 0.27 0.76 97 0.26 0.80 91 523.6 × 1010 |
| SS-2(25%) |
| ______________________________________ |
From Table VIII it is apparent that a speed enhancement can be realized with a proportion of SS-2 of only 5 mole percent, based on total spectral sensitizing dye. A preferred proportion of dye having a more negative reduction potential is up to 20 mole % of the total dye, although a proportion of SS-2 of up to 35 mole % is shown to be advantageous in Example 7.
This demonstrates that the addition of a SET dopant to the AgCl epitaxy can be relied upon to further increase photographic speed.
An emulsion was prepared, coated, exposed and processed similar as CT-6, except that the sensitization was varied by adding SET-11 during deposition of the AgCl epitaxy in the concentrations set out in Table IX and the sensitization was varied as follows: Formation of the second epitaxial phase spectral sensitizing dye SS-1 was added in the amount of 0.39 mmole per silver mole. Then to each sample were added at 40° C. in sequence the following reagents in millimoles per silver mole with 5 minute holds between each successive addition: 0.617 mmole of NaSCN, 0.0355 mmole of N,N'-dicarboxymethyl-N,N'-dimethylthiourea, 0.0070 mmole of Au(I) bis(trimethylthiotriazole), and 2.5 mg of 3-methyl-1,3-benzothiazolium iodide. Chemical sensitization was effected by raising the emulsion melt containing addenda to 50°C and holding for 7.5 minutes. Subsequently, the melt was cooled to 40° C., and 0.6453 millimole of 1-(3-acetamidophenyl)-5-mercaptotetrazole (APMT) was introduced. The melt was then prepared for coating.
The results are summarized in Table IX.
| TABLE IX |
| ______________________________________ |
| Dopant Level Relative |
| (mppm ΣAg) Speed Gamma |
| ______________________________________ |
| 0 100 0.42 |
| 1.5* 106 0.63 |
| ______________________________________ |
| *Introduced in first 25% of AgCl epitaxy |
The SET-11 dopant increased speed and contrast when incorporated in a concentration of 1.5 molar parts per million (mppm), based on total silver forming the grains. The local concentration of the dopant within the AgCl epitaxy was 18.75 mppm.
This demonstrates that the addition of a SET dopant to the host tabular grains can be relied upon to further increase photographic speed.
Example 9 was repeated, except that the SET dopant, SET-2, was added only during precipitation of the host tabular grains. Dopant addition began after precipitation of X% of total silver forming the host tabular grains and was terminated when Y% of the total silver had been precipitated. See Table X below for actual X and Y values. The local concentration of the SET-2 dopant was 250 mppm in all instances. Additionally, the concentrations of the chemical sensitizers were varied as follows: 1.851 mmole of NaSCN, 0.0178 mmole of N,N'-dicarboxymethyl-N,N'-dimethylthiourea, and 0.0035 mmole of Au(I) bis(trimethylthiotriazole). Spectral sensitization was varied by adding a 15% SS-2 and 85% SS-5 mixture after holding at 50°C for 7.5 minutes.
The results with and without SET-2 dopant are summarized in Table X.
| TABLE X |
| ______________________________________ |
| X Y Dmin Gamma Rel. Speed |
| ______________________________________ |
| no 0.27 0.94 100 |
| dopant |
| 1 30 0.23 0.95 110 |
| 30 60 0.19 0.94 118 |
| 1 60 0.20 0.88 122 |
| 60 90 0.21 0.97 108 |
| ______________________________________ |
From Table X it is apparent that the SET dopant increased photographic speed and lowered minimum density. Contrast was also increased, except when the amount of SET dopant was doubled by extending dopant introduction over the range of from 1 to 60 percent of the silver addition.
This demonstrates the adsorption and photographic advantages to be realized by employing high iodide plates on the major faces of ultrathin (t<0.07 μm) host tabular grains.
A silver iodobromide host tabular grain emulsion was prepared by first charging a reaction vessel with 1.25 g/L of oxidized gelatin, 0.625 g/L NaBr, 0.7 mL of a polyethylene glycol surfactant suspended with paraffin oil in a naphthenic distillate(NALCO 2341™) and 6 L of distilled water. The contents of the reaction vessel were adjusted to a pH of 1.8 at 45°C Nucleation occurred during a five second period during which 1.67 m/L of AgNO3 and 1.645 mole/L of NaBr and 0.02505 mole/L KI were each added at a rate of 110 mL/min. The temperature was then adjusted to 60°C and held for nine minutes. An additional 100 g of oxidized gelatin were added to the reactor, and the pH was then adjusted to 5.85 with NaOH. Subsequently 0.098 mole of NaBr was introduced into the reaction vessel such that the pBr was brought to 1.84. A further pBr shift to 1.517 was produced by the single jet addition of 1.75 mole/L of NaBr at 61.3 mL/min for 1.5 minutes. The remainder of the emulsion was precipitated over a period of 66 minutes using a triple jet. This triple jet consisted of 1.66 mole/L of silver nitrate accelerated from 12.5 to 96 mL/minute, 1.75 mole/L of NaBr accelerated from 13.3 to 95.6 mL/minute, and 136.25 g Ag/L of a fine grain AgI Lippmann emulsion accelerated from 12.5 to 96 mL/min. The emulsion was then cooled to 40°C, iso-washed twice and adjusted to a pBr of 3.378 and a pH of 5.6.
The resulting AgIBr tabular grain emulsion contained 2.5% bulk iodide and had a grain size COV of 52 percent. The mean ECD of the emulsion grains was 2.9 μm, and the mean thickness of the grains was 46 nm. The average aspect ratio of the tabular grains was 63. Greater than 90 percent of total grain projected area was accounted for by tabular grains.
This emulsion, described above, was employed to compare the absorption of the ultrathin tabular grain emulsion UT/HT-11 with a thicker host tabular grain emulsion.
UT-11+AgI36 Br64 (9.2M% I)
Silver iodobromide was precipitated on the major faces of a sample of the ultrathin tabular grains of UT/HT-11 in amount sufficient to provide an additional 9.2 mole % iodide.
UT-11+AgI(9.2M% I)
A high iodide phase was deposited on the major faces of a sample of the ultratin tabular grains of UT/HT-11 using the procedure used for the preparation of CT-2, but with the amount of additional AgI precipitated adjusted to 9.2M%, based on total silver.
UT-11+AgI(40M% I)
A high iodide phase was deposited on the major faces of a sample of the ultratin tabular grains of UT/HT-11 using the procedure used for the preparation of CT-2, but with the amount of additional AgI precipitated adjusted to 40M%, based on total silver.
UT-11+AgI(55M% I)
A high iodide phase was deposited on the major faces of a sample of the ultratin tabular grains of UT/HT-11 using the procedure used for the preparation of CT-2, but with the amount of additional AgI precipitated adjusted to 55M%, based on total silver.
A sample of each of the emulsions above was coated at 10.76 mg/dm2 silver with an equal volume of gelatin on a cellulose acetate photographic film support with an antihalation backing layer. The emulsion layer was overcoated with 21.53 mg/clm2 of gelatin containing 1.5 percent, by weight, based on total gelatin, of bis(vinylsulfonyl)methane hardener.
Light absorption was determined as described above in Example 2. The results are shown below in Table XI.
| TABLE XI |
| ______________________________________ |
| Emulsion Integrated Light |
| Sample Absorption photons/sec/cm2 |
| ______________________________________ |
| HT-2 294 × 1010 |
| UT-11 317 × 1010 |
| UT-11 + AgI36 Br64 (9.2 M % I) |
| 857 × 1010 |
| UT-11 + AgI(9.2 M % I) |
| 966 × 1010 |
| UT-11 + AgI(40 M % I) |
| 1545 × 1010 |
| UT-11 + AgI(55 M % I) |
| 1778 × 1010 |
| ______________________________________ |
Table XI demonstrates that the ultrathin tabular grains (UT-11) even without further iodide addition demonstrated higher absorptions than the host tabular grains HT-2, even though HT-2 contained a higher percentage of iodide than UT-11. When AgIBr containing a near-saturation level of iodide was deposited on the UT-11 tabular grains, absorption was increased markedly, but not to as great an extent as when the same amount of iodide was deposited as a high iodide phase.
Table XI further demonstrates that much higher levels of iodide can be deposited on the major faces of the host UT-11 tabular grains and that absorption is further markedly increased. This demonstrates the feasibility increasing the proportion of total silver deposited in the high iodide phase to near 60 percent.
Sensitometric evaluation of UT-11, UT-11+AgI36 Br64 (9.2M% I) and UT-11+AgI(9.2M% I) was conducted as described in Example 6 for 3000° K. exposures, except that sensitization of UT-11 was varied to achieve optimization as follows: The addition of 1.54 mmoles of NaSCN then 1.336 mmoles of spectral sensitizing dye SS-23 was followed by the addition of 0.034 mmole of N,N'-dicarboxymethyl-N,N'-dimethylthiourea and then 0.00439 mmole of Ag(I)bis(trimethylthiotriazole). A heat cycle of 7.5 minutes at 50°C was employed. The sensitizations of emulsions UT-11+AgI36 Br64 (9.2M% I) and UT-11+AgI(9.2M% I) were identical to that of UT-11, except that the concentration of N,N'-dicarboxymethyl-N,N'-dimethylthiourea was reduced to 0.023 mmole. The sensitizations of the latter two emulsions were undertaken without further optimization, thereby providing a comparison favoring emulsion UT-11.
The performance of the emulsions is summarized in Table XII.
| TABLE XII |
| ______________________________________ |
| 3000° K. |
| Emulsion Dmin Gamma Speed |
| ______________________________________ |
| UT-11 0.08 2.31 100 |
| UT-11 + 0.1 0.62 38 |
| AgI36 Br64 (9.2 M % I) |
| UT-11 + 0.12 0.41 108 |
| AgI(9.2 M % I) |
| ______________________________________ |
From Table XII it is apparent that applying iodide to the face of the ultrathin tabular grains in the form of a AgIBr markedly decreased the speed of the emulsion. The reason for this was that the AgIBr could only be applied as a continuous shell over the exterior surface of the host tabular grains. On the other hand, the same amount of iodide deposited on the major faces of the host tabular grains as discrete plates left a large percentage of the host tabular grain surface unoccupied. This allowed the higher light absorption made possible by the high iodide plates to be translated into an increased photographic speed.
This demonstrates the application of the invention to low (<5) aspect ratio tabular grain emulsions.
PAC Host Tabular Grain Emulsion LHT-12An AgIBr low aspect ratio host tabular grain emulsion was prepared by first charging a reaction vessel with 1.5 g/L of oxidized gelatin, 0.6267 g/L NaBr, 0.15 g/L of the surfactant block copolymer A (see Example 1) and 6 L of distilled water. The contents of the reaction vessel were adjusted to a pH of 1.85 at 40°C After a temperature adjustment to 45° C. nucleation occurred during a one minute period in which 0.8 mole/L of AgNO3 and 0.84 mole/L of NaBr were each added at a rate of 97.2 mL/min. The halide excess in the reactor was increased by introducing an additional 0.115 mole of NaBr. The temperature was then adjusted to 60°C over 9 minutes. A 9 minute ammoniacal digest ensued by the addition of 0.153 mole of ammonium sulfate activated by a pH adjustment to 9.5 by the addition of NaOH. An additional 100 g of oxidized gelatin were added to the reactor along with 1 g of block copolymer A, and pH was then adjusted to 5.85 with HNO3. A first growth segment occurred over 5 minutes during which the AgNO3 and KBr reagents used for nucleation were introduced each at 9 mL/min at a pBr of 1.776. A second growth segment occurred over a nine minute period at this pBr and temperature by introducing 1.6 mole/L AgNO3 at a linearly accelerated rate of from 9 to 19 mL/min and 1.679 mole/L of NaBr at a linearly accelerated rate of from 4.7 to 16.9 mL/min. This was followed by a third growth segment of 54 minutes at an elevated pBr of 2.633 continuing with the same reactants, but at linearly accelerated rates of from 20.1 to 80 mL/min for AgNO3 and 19.4 to 76.7 mL/min for NaBr. A final growth segment using the same reactants lasted 18.5 minutes at a constant flow rate of 80 mL/min. The emulsion was then cooled to 40°C, iso-washed twice and adjusted to a pBr of 3.378 and a pH of 5.5.
The resulting AgBr tabular grain emulsion had a grain size COV of 11 percent. The average ECD of the emulsion grains was 0.78 μm and the average thickness of the grains was 0.25 μm. The average aspect ratio of the tabular grains was 3. Greater than 90 percent of total grain projected area was accounted for by tabular grains.
A 4 liter vessel was charged with one mole of host tabular grain emulsion and 1200 mL of distilled water, allowed to equilibrate at 40°C for 10 minutes and then brought to a temperature of 60°C The pBr was then raised from 3.681 to 5.261 during the first 3 minutes of a 15 minute segment in which a double jet addition of 0.25M AgNO3 reagent was introduced at a linearly accelerated rate of from 2.3 to 11.6 mL/min while a 0.3M KI solution was introduced at a linearly accelerate rate of from 3.3 to 16.5 mL/min.
A second growth segment at the same pBr followed lasting 15 minutes in which the AgNO3 was ramped from its final value in segment I to a value of 23.1 mL/min while the KI reagent flow rate was accelerated to 33 mL/min. The emulsion was subsequently iso-washed twice.
An overall bulk iodide content of 8.8 mole percent was found by neutron activation analysis. The silver iodide phase formed thin plates on the major faces of the host tabular grains. The plates consisted essentially of β phase AgI.
This emulsion was prepared similarly as CT-12A, except that a higher bulk iodide level, 21.2 mole percent, based on total silver, was found by neutron activation analysis. The higher iodide content resulted from a 27.5 minute third growth segment of constant flow rates 23.1 and 33.0 mL/min for AgNO3 and KI, respectively.
This emulsion was prepared similar as CT-12B, except that a still higher bulk iodide level, 32.9 mole percent, based on total silver, was found by neutron activation analysis. The higher iodide content resulted from extending the third growth segment of CT-12B to 79.5 minutes.
Two samples of each of the emulsions above, one without spectral sensitizing dye and one containing SS-23 at 433.2 mg/Ag mole, were coated at 10.76 mg/dm2 silver with an equal volume of gelatin on a cellulose acetate photographic film support with an antihalation backing layer. The emulsion layer was overcoated with 21.53 mg/dm2 of gelatin containing 1.5 percent, by weight, based on total gelatin, of bis(vinylsulfonyl)methane hardener.
Light absorption was determined as described above in Example 2. The results are shown below in Table XIII.
| TABLE XIII |
| ______________________________________ |
| Undyed Integrated |
| SS-23 Integrated Light |
| Light Absorption |
| Absorption |
| Emulsion (Iodide M %) |
| photons/sec/cm2 |
| photons/sec/cm2 |
| ______________________________________ |
| CT-12A (8.8) 671.4 × 1010 |
| 1076 × 1010 |
| CT-12B (21.2) |
| 981.8 × 1010 |
| 1191.2 × 1010 |
| CT-12C (32.9) |
| 1111.7 × 1010 |
| 1270.6 × 1010 |
| ______________________________________ |
By comparison with Table II, which demonstrates absorptions, with and without SS-23, of 20.6 mole percent iodide on a high aspect ratio tabular grain host, it is apparent that the low aspect ratio tabular grain host was also effective to produce high levels of light absorption.
This example demonstrates the increase in speed and reduction in minimum density that can be realized by adding FCCRS silver halide over the first epitaxial phase.
Host tabular grain emulsion HT-6 was prepared as described in Example 6 and, following the procedure of that example, HT-6 was used to prepare composite tabular grain emulsion CT-6 by growing a restricted high iodide first epitaxial phase on the host tabular grains.
A sample of emulsion CT-6 was then shelled by the following procedure: A 0.5 mole aliquot of CT-6 was melted at 40°C at a pBr of 3.4263. A double-jet precipitation of 0.5M silver nitrate and 0.5 mixed halide salts (0.15M sodium bromide and 0.35M sodium chloride) was then performed at a controlled pBr of 3.700 for 4.3 minutes at a fixed flow rate of 11.5 mL/min. Under these conditions only silver bromide accounting for 1.5 percent of total precipitates. If uniformly distributed, this would amount to a coating of about 3 to 4 atomic planes in thickness. The resulting emulsion is hereinafter referred to as CT-6+1.5AgBr.
Samples of each of CT-6 and CT-6+1.5AgBr were next sensitized as follows: A 800 mL reaction vessel was charged with a 0.5 mole sample (based on the silver in the tabular host grains). The addition of 0.25N silver nitrate was then used to raise the pBr of the sample from 3.394 to 7.022 at 40°C A small amount of KI, 0.5 mole percent, based on silver, was then added. This was followed by 4 mole percent sodium chloride, based on silver. The emulsion samples were then spectrally sensitized with a combination of SS-10 (0.39 mmole) and SS-2 (0.069 mmole). A double-jet precipitation of 1.0M silver nitrate and 1.0M sodium chloride was 30.1 mL/min for 1.33 minutes produced corner epitaxial deposits of 8 mole percent, based on total silver, almost exclusively at the corners of the grains. The pBr of the emulsion samples at the end of the silver chloride double-jet precipitation was 3.7.
The following chemical sensitization of CT-6 and CT-6+1.5AgBr samples were then undertaken at 40°C, described on a one mole basis-in mmole/Ag mole: Sequentially with 5 minute holds between each addition 1.235 mmole of sodium thiocyanate, 0.0226 mmole of N,N'-dicarboxymethyl-N,N'-dimethylthiourea, 0.0031 mmole of Au(I)bis(trimethyl thiotriazole) and 2.5 mg of 3-methyl-1,3-benzothiazolium iodide. Chemical sensitization was effected by raising the samples to 50°C and holding for 5 minutes. Subsequently, the melt was cooled to 40°C and 0.6453 millimole of APMT.
Single emulsion layer coatings were formulated containing 10.76 mg/dm2 silver halide, 16.14 mg/dm2 of gelatin, and 9.684 mg/dm2 of the yellow dye-forming coupler YC-1. The emulsion layer also contained 1.75 g/silver mole of 4-hydroxy-6-methyl-1,3,3a,7-tetraazaindene. The emulsion layer was coated on a transparent film support and overcoated with 10.76 mg/dm2 gelatin and hardened with 1.5% by weight, based on total gelatin weight in both layers, of bis(vinylsulfonyl)methane.
Samples of the coatings were exposed through a 0-4 density step tablet for 1/50" using a Wratten 2B™ filter (to eliminate <390 nm wavelengths) with a 0.6 neutral density inconel filter and a 3000° K. color temperature (tungsten balance) light source. The exposed coatings were developed for 3.25 minutes using the Kodak ECN-2 process, described in Kodak H-24 Manual, Manual for Processing Eastman Motion Picture Films.
The sensitometric results are summarized in Table IX.
| TABLE IX |
| ______________________________________ |
| Emulsion Dmin Gamma Speed* |
| ______________________________________ |
| CT-6 0.34 0.78 100 |
| CT-6 + 1.5AgBr |
| 0.23 0.78 110 |
| ______________________________________ |
| *inertial speed |
From Table IX it is apparent that the FCCRS surface silver halide lowered minimum density and raised speed by 0.1 log E.
Other samples of the coatings were also given a exposures at 10 nm increments from 360 to 510 nm using a wide range spectral sensitometer. Development was as described above. Speed in 1/ergs/cm2 /sec at each wavelength of exposure is shown in FIG. 10. From FIG. 1 it is apparent that CT-6+1.5AgBr (curve E) exhibited a speed advantage over CT-6 (curve C) at all wavelengths less than 510 nm.
This demonstrated conclusively performance advantages for the addition of surface FCCRS silver halide.
The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.
Reed, Kenneth Joseph, Hansen, Jeffrey Christen
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